depends on what kind of applications you're planning on using on it and if your windows 7 is 64bit or not. personally i'd go with windows 7 (i don't think there's a adobe flash player for it though that works 100%) because windows xp is old, and is a breeding ground for viruses and other junk. there's also a new version of bootcamp that has windows 7 drivers that you can get off of apple's site and install it once windows is up and running.