this depends on how different the documents can be, and how do you want to look at the differences.
Basicly it are all xml documents inside, if you only expect relative minor differences (like a change in text, font change, etc..) you could do a diff at that level (presumably even with your windiff application).
If you really want a graphical view of the differences (to see image and color changes and so on), I think the best way is to convert the files to a pixel format and do a diff on that.
I do not know of a tool for the moment that does the latter automatically for xps.
Regards,
nixps
Yes, there's a cool tool "diffOPC" I only can recommend, try out yourself...
you can get it here... http://www.arstdesign.com/articles/diffopc.htmlhope this helps...
regards,
Jo