It sounds like you are missing pygtk. As a test you can go into the 'x terminal' and enter 'python'. When python shell starts (you will see the '>>>' prompt) then type 'import gtk' and see if there are errors. If you are missing pygtk, try installing an application that uses pygtk should install the dependency. Not sure which programs will do that (I have lot of applications already installed so it is hard to tell).

PyGTKEditor has weird dependency problems, I had python25-gtksourceview installed and pygtkeditor wouldn't install with it, so I edited the pygtkeditor deb data files to remove the dependency and it installed and worked perfectly.