Needing to use a GtkFixed is rare. Usually, by packing widgets into containers and appropriately setting packing options, borders, padding, etc. you can achieve what you want with less coding.
It's tricky for a new GTK+ developer as the concepts of widget allocation and packing are new. You'll want to read up on it and experiment with the "expand" and "fill" packing properties.
Below a glade file showing what I think you're trying to do. The labels in the left column of the GtkTable have expand set to false, so that column is as big as the largest label. The widgets in the right column have horizontal expanding TRUE so that they fill the rest of the space.
The GtkHBox is packed into a viewport packed into a GtkScrolledWindow. When the window is resized below a size which allows all the widgets to be viewed, then scrollbars will appear.
example.glade
Code:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE glade-interface SYSTEM "glade-2.0.dtd">
<!--Generated with glade3 3.4.0 on Wed Dec 19 12:36:21 2007 -->
<glade-interface>
<widget class="GtkWindow" id="window1">
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<child>
<widget class="GtkScrolledWindow" id="scrolledwindow1">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="hscrollbar_policy">GTK_POLICY_AUTOMATIC</property>
<property name="vscrollbar_policy">GTK_POLICY_AUTOMATIC</property>
<child>
<widget class="GtkViewport" id="viewport1">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="resize_mode">GTK_RESIZE_QUEUE</property>
<child>
<widget class="GtkTable" id="table1">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="n_rows">9</property>
<property name="n_columns">2</property>
<property name="column_spacing">6</property>
<property name="row_spacing">2</property>
<child>
<widget class="GtkEntry" id="entry4">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
</widget>
<packing>
<property name="left_attach">1</property>
<property name="right_attach">2</property>
<property name="top_attach">8</property>
<property name="bottom_attach">9</property>
<property name="y_options"></property>
</packing>
</child>
<child>
<widget class="GtkEntry" id="entry3">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
</widget>
<packing>
<property name="left_attach">1</property>
<property name="right_attach">2</property>
<property name="top_attach">7</property>
<property name="bottom_attach">8</property>
<property name="y_options"></property>
</packing>
</child>
<child>
<widget class="GtkEntry" id="entry2">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
</widget>
<packing>
<property name="left_attach">1</property>
<property name="right_attach">2</property>
<property name="top_attach">6</property>
<property name="bottom_attach">7</property>
<property name="y_options"></property>
</packing>
</child>
<child>
<widget class="GtkColorButton" id="colorbutton1">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="receives_default">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_MOTION_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="response_id">0</property>
<property name="color">#000000000000</property>
</widget>
<packing>
<property name="left_attach">1</property>
<property name="right_attach">2</property>
<property name="top_attach">5</property>
<property name="bottom_attach">6</property>
<property name="y_options"></property>
</packing>
</child>
<child>
<widget class="GtkFontButton" id="fontbutton1">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="receives_default">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="response_id">0</property>
</widget>
<packing>
<property name="left_attach">1</property>
<property name="right_attach">2</property>
<property name="top_attach">4</property>
<property name="bottom_attach">5</property>
<property name="y_options"></property>
</packing>
</child>
<child>
<widget class="GtkToggleButton" id="togglebutton1">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="receives_default">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="label" translatable="yes">togglebutton</property>
<property name="response_id">0</property>
<property name="active">True</property>
</widget>
<packing>
<property name="left_attach">1</property>
<property name="right_attach">2</property>
<property name="top_attach">3</property>
<property name="bottom_attach">4</property>
<property name="y_options"></property>
</packing>
</child>
<child>
<widget class="GtkComboBox" id="combobox1">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
</widget>
<packing>
<property name="left_attach">1</property>
<property name="right_attach">2</property>
<property name="top_attach">2</property>
<property name="bottom_attach">3</property>
<property name="y_options"></property>
</packing>
</child>
<child>
<widget class="GtkSpinButton" id="spinbutton1">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="adjustment">0 0 100 1 10 10</property>
</widget>
<packing>
<property name="left_attach">1</property>
<property name="right_attach">2</property>
<property name="top_attach">1</property>
<property name="bottom_attach">2</property>
<property name="y_options"></property>
</packing>
</child>
<child>
<widget class="GtkEntry" id="entry1">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
</widget>
<packing>
<property name="left_attach">1</property>
<property name="right_attach">2</property>
<property name="y_options"></property>
</packing>
</child>
<child>
<widget class="GtkLabel" id="label10">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="xalign">1</property>
<property name="label" translatable="yes">Label:</property>
</widget>
<packing>
<property name="top_attach">8</property>
<property name="bottom_attach">9</property>
<property name="x_options">GTK_FILL</property>
<property name="y_options">GTK_FILL</property>
</packing>
</child>
<child>
<widget class="GtkLabel" id="label9">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="xalign">1</property>
<property name="label" translatable="yes">Label:</property>
</widget>
<packing>
<property name="top_attach">7</property>
<property name="bottom_attach">8</property>
<property name="x_options">GTK_FILL</property>
<property name="y_options">GTK_FILL</property>
</packing>
</child>
<child>
<widget class="GtkLabel" id="label8">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="xalign">1</property>
<property name="label" translatable="yes">Label:</property>
</widget>
<packing>
<property name="top_attach">5</property>
<property name="bottom_attach">6</property>
<property name="x_options">GTK_FILL</property>
<property name="y_options">GTK_FILL</property>
</packing>
</child>
<child>
<widget class="GtkLabel" id="label7">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="xalign">1</property>
<property name="label" translatable="yes">Label:</property>
</widget>
<packing>
<property name="top_attach">6</property>
<property name="bottom_attach">7</property>
<property name="x_options">GTK_FILL</property>
<property name="y_options">GTK_FILL</property>
</packing>
</child>
<child>
<widget class="GtkLabel" id="label6">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="xalign">1</property>
<property name="label" translatable="yes">Label:</property>
</widget>
<packing>
<property name="top_attach">4</property>
<property name="bottom_attach">5</property>
<property name="x_options">GTK_FILL</property>
<property name="y_options">GTK_FILL</property>
</packing>
</child>
<child>
<widget class="GtkLabel" id="label5">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="xalign">1</property>
<property name="label" translatable="yes">Label with more chars:</property>
</widget>
<packing>
<property name="top_attach">3</property>
<property name="bottom_attach">4</property>
<property name="x_options">GTK_FILL</property>
<property name="y_options">GTK_FILL</property>
</packing>
</child>
<child>
<widget class="GtkLabel" id="label4">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="xalign">1</property>
<property name="label" translatable="yes">Label:</property>
</widget>
<packing>
<property name="top_attach">1</property>
<property name="bottom_attach">2</property>
<property name="x_options">GTK_FILL</property>
<property name="y_options">GTK_FILL</property>
</packing>
</child>
<child>
<widget class="GtkLabel" id="label3">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="xalign">1</property>
<property name="label" translatable="yes">Label:</property>
</widget>
<packing>
<property name="top_attach">2</property>
<property name="bottom_attach">3</property>
<property name="x_options">GTK_FILL</property>
<property name="y_options">GTK_FILL</property>
</packing>
</child>
<child>
<widget class="GtkLabel" id="label1">
<property name="visible">True</property>
<property name="events">GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK | GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK</property>
<property name="xalign">1</property>
<property name="label" translatable="yes">Label:</property>
</widget>
<packing>
<property name="x_options">GTK_FILL</property>
<property name="y_options">GTK_FILL</property>
</packing>
</child>
</widget>
</child>
</widget>
</child>
</widget>
</child>
</widget>
</glade-interface>