You don't need gtk-builder-convert if you save your Glade project as GtkBuilder XML. It can be loaded directly into GTK in more recent GTK versions. It's fine to name the file with a .glade extension.
I'll just add that you can nominate callbacks for early lifecycle events like "realize" in a GtkBuilder UI definition. Realize fires when a widget is constructed, but before it is mapped (has a screen area (GdkWindow) allocated to it) and before it's shown. This is useful for all sorts of fancy fiddling while keeping the conceptual neatness described by saunderson: all you need to do in the code is define a callback matching the one you named, at least in high-level stuff like Python:
class DemoBehaviour (object):
self.builder = Gtk.Builder()
window = self.builder.get_object("window1")
def window1_realize_cb(self, widget):
print "* realized"
as a thumbnail sketch. Glade suggests names for the callback functions or methods, when you set them up on the Signals tab.