what is your psu..?
if you let your computer stay idle for a long time, did bsod still occur?
or it was happening while you did something like load heavy programs..?
how many memory stick do you have..?
remove one of memory stick and see..
if bsod still occur, change to the other stick..
your memory maybe defective..
if problem still occur..download hiren boot cd from this site..http://www.hirensbootcd.org/download/
this is a live cd utility that you can run a operating system from your cd or thumb drive, not from your harddisk..
run win xp from the cd, and computer stay idle for a long time or do any activities on it, any bsod still occur?