GNU emacs feature

Hi: I have used both GNU Emacs and XEmacs and there is a feature in GNU Emacs that I don't see in XEmacs. It might be that I just don't know how to do it in XEmacs. The feature is as follows: In GNU Emacs, the user can have two buffers open with different files and then do a diff between the two files. The user can do this by choosing Tools->Compare->Two Buffers... The user then hits enter twice to select both buffers that are displayed. The differences are then highlighted in the two buffers. Do you know if there is a way to do this in XEmacs? Thanks, Chris Foulds