Yes, This is completely possible. I write such applications. This is my work.
You can even write and compile the windoze version of the program without to leave linux.The built exe is ready to use on windoze.
Just download and install MinGW environment and the GTK+ runtime environment for windoze.
If you use Fedora just install these RPMs for MinGW.
http://mirzam.it.vu.nl/mingw/
Then install this self-extract package.
http://www.nhydra.org/files/GTK%20Platform%20Win32-1.0-Linux-x86-Install
There is available some installers on this address
http://www.nhydra.org/ for GTK and MinGW on both Windoze and Linux
And then use this script to compile and build your GTK+ Win32 Application.
#!/bin/sh
EXEC_COMMAND="i386-mingw32-gcc"
# Base GTK Platform install path
GTK_BASE_PATH="/home/work_user/gtk-win32-platform"
# GTK Binary directory
GTK_BIN_DIR="base"
#GTK development directory
GTK_DEV_DIR="base-dev"
# Execute the compiling
echo "Additional source files: $@"
$EXEC_COMMAND main.c callbacks.c interface.c support.c $@ \
-o gtk-win32-out.exe \
-mms-bitfields \
-I$GTK_BASE_PATH/$GTK_DEV_DIR/include/ \
-I$GTK_BASE_PATH/$GTK_DEV_DIR/include/atk-1.0 \
-I$GTK_BASE_PATH/$GTK_DEV_DIR/include/cairo \
-I$GTK_BASE_PATH/$GTK_DEV_DIR/include/freetype2 \
-I$GTK_BASE_PATH/$GTK_DEV_DIR/include/glib-2.0 \
-I$GTK_BASE_PATH/$GTK_DEV_DIR/lib/glib-2.0/include \
-I$GTK_BASE_PATH/$GTK_DEV_DIR/include/gtk-2.0 \
-I$GTK_BASE_PATH/$GTK_DEV_DIR/lib/gtk-2.0/include \
-I$GTK_BASE_PATH/$GTK_DEV_DIR/include/pango-1.0 \
-L$GTK_BASE_PATH/$GTK_DEV_DIR/lib \
-latk-1.0 \
-lcairo \
-lfreetype \
-lgettextpo \
-lgtk-win32-2.0 \
-lglib-2.0 \
-lgdk-win32-2.0 \
-lgdk_pixbuf-2.0 \
-lgobject-2.0 \
-lgmodule-2.0 \
-lgthread-2.0 \
-lpango-1.0 \
-lzdll
If you need more particular information just PM me... I am very interested for developing GTK+ apps on both Windoze and Linux so I will be very glad to contact you.
I am wondering about creating of such user group...