Araxis merge works fine in xp here is a link to a 30 day free trial. If you want to buy it you can get 20 people on the same access code so you might be able to get a group togehter and share the cost.
https://logic.araxis.com/CustomerSup...valuationF.xml
Here is winmerge
http://winmerge.sourceforge.net/
http://prdownloads.sourceforge.net/w...e.zip?download