If you shut off the System Restart on error feature it will give the BSOD instead of rebooting. THis will give you an error code that's easier (for me at least) to decipher the hardware issue.
I would begin by removing all but onestick of RAM and seeing if it persists, this is VERY common for dead RAM.
In fact, I would almost put money on it that the RAM is failing or dead. But a BSDO would help ME a bit mroe. Chas or Colin will probably be able to help with the POST error.
I took it to DEJA.COM and there are several similar questions but no answers except one that points to a seemingly different XP boot issue:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;q317277