XP's native defragger is called "Diskeeper Lite". The full version, "Diskeeper 7.0", is much better. It costs $39.95, but you can get a 30 day free trial here. Try it. If you don't like it there are others like "PerfectDisk" by Raxco.
http://consumer.execsoft.com/diskeep...per.asp?RId=50
http://www.raxco.com/