Solution found!
Not only would this make it more multi-platform (I have no access to a GTK machine so I don't know if this works. Could someone please check?)
Looks like it works (I had to change frame.Show() to frame.Show(1) though, but that could be because it's an old version). One odd thing though: the Windows version doesn't react to clicking or dragging the mouse, which seems to be the expected behavior. The GTK version can be moved by dragging the mouse; even just clicking the mouse moves the window somewhat down and to the left.
-- "Codito ergo sum" Roel Schroeven -- http://mail.python.org/mailman/listinfo/python-list
