The new versions of PyGTK (see faq 2.1) provide a pygtk module in which you can call a method require() that allows you to request one version or the other:

 pygtk.require("1.2") # for pygtk-0

and

 pygtk.require("2.0") # for pygtk2

Note that you should do this before importing the gtk or gnome modules:

 # To require 2.0 
 import pygtk
 pygtk.require("2.0")
 import gtk, gtk.glade, gnome, gnome.ui

or:

 # To require 1.2
 import pygtk
 pygtk.require("1.2")
 import gtk, libglade, gnome, gnome.ui

If this simply doesn't work, please visit FAQ 2.6 for the nitty-gritty.