I figured it out after finding an example somewhere:
>>> import Tix
>>> app = Tix.Tk("Demo")
>>> panes = Tix.PanedWindow(app)
>>> left = panes.add('left')
>>> right = panes.add('right')
>>> tree = Tix.Tree(left)
>>> notebook = Tix.NoteBook(right)
>>> tree.pack()
>>> notebook.pack()
>>> panes.pack()
>>> app.mainloop()-- http://mail.python.org/mailman/listinfo/python-list
