1. As acid_kewpie points out, you should be using GTK+ 2.0/GDK, not the older GTK+ 1.0 library. I presume you're already doing so.
2. In addition to the standard debugging tools (gdb, "printf", etc etc), GTK+ 2.0 also has some nice built-in capabilities, notiably
using the GDK_DEBUG environment variable and the gdk-debug compiler flag:
'Hope that helps .. PSM