Do you mean, you’d like to get rid of Vista and only have XP? or do you want both? In the case of the former, all you have to do is format your harddrive and put in an XP install disk. If you want to have both operating systems, it’s a bit more effort. The process is typically called Dual booting and there are tons of sites that could walk you through it. I’ve never done it with Vista, so I can’t really give any personal tales about how hard/easy it was.