OK. You need to download Magical Jelly Bean Keyfinder (http://www.majorgeeks.com/download.php?det=2612
). This will retrieve his Windows key from his registry.
Once you have done that, you can format and reinstall Windows from any XP disk, and use his own key code.
If, however you choose to try to salvage the OS and all, go here:
and read the list. Download what if calls for and take it with you.
Once you get things cleaned up a little, go online and go to http://housecall.trendmicro.com/
with Internet Explorer. Do the free online scan.
Be sure to download and install a decent firewall on the computer, as well as antivirus.