Windows XP can be installed, however trying to get a computer system to do so can be tough. The best way to do so is to format the hard drive, or get a different hard drive, and do a complete install of XP on it. Windows XP runs anywere from $100-300 depending on where you get it and which version you get. Most users can get away with Windows XP Home Edition as that's what I used to use before I started liking Vista. Personally I can't see a huge difference between the 2 useability wise. I think Vista is a bit more stable though.