Format

Assuming you have backed uip all of your files you do this:

1 - reset your computer and as soon as it powers off repeatedly press del, f2, f8 (one of those buttons will send you to SETUP, impossible to know which one although i think its usually del)

2 - go to the BOOT menu, and change the settings so that the primary BOOT device is the DVD drive

3 - insert your windows XP disc

4 - reset your computer and follow the onscreen instructions!
 
lets not forget that while all the steps are right, he might need drivers for the Sata controller, and have them on a stiffy disk.

if the XP setup comes up with a error saying it cant find any hardrives. You gonna need the driver.