Wipe the hard-drive, re-partition with the XP SP2 CD and FULL format the first partition before installing. Other partitions can be made and formatted using XP's Disk Mangement.
I would run the drive manufacturer's diagnostic diskette over the drive and run a test on the RAM modules as a matter of course. If the RAM modules need to be re-seated now is the time and then all duxst and debris can be cleaned out of the casing and all fans, etc. checked.
See link below for more info.