I split this off from the thread that dely0575 posted this question in because he changed the subject.
I would recommend XP. I have had to program for Vista and there are still many problems with Vista. Even if they fix all of the problems in Vista, Vista still is way too protective in an obnoxious way (which means that either you turn off all of the protection which leaves you unprotected, or you spend a lot of time giving your permission to run processes). Vista also is a hog of resources (which is the Microsoft mentality) and so you need a much bigger and faster computer to do the things that you do in XP at the same speed.
Vista does look good and is neat, but I don't think the bells and whistles are worth the hassle.