rickity, good advice - except that you can't get a BSOD during BIOS checks, as Windows hasn't yet loaded!
Assuming it isn't a hardware fault -
Is it possible to boot in safe mode and roll back via system restore to a date when the system was operational (before the hardware or software was added that is causing the problem)?
Depends on whether or not Safe Mode is available (i.e. doesn't BSOD in safe mode) and if suitable SR points are available.
Also possible to Repair Windows XP via install CD.
Or reinstall Win XP over existing - inelegant but effective (backup of data and profiles essential).
Usually is some useful info on the BSOD - try taking a photo with a digital camera or note down any filenames that are mentioned - may be possible to replace them if corrupt. You can use the recovery console if you are brave - not for the faint-hearted!
SD