OK… You’ve eliminated everything except your AGP video card, so that might be the next best logical place to look….
The STOP: error you are receiving (PAGE_FAULT_IN_NON-PAGED_AREA). Several MS Technet articles point to defective RAM, cache or <i>video memory</i> as the probable cause. Since you appear to have eliminated the other causes of this error, I would strongly suspect video memory…
If you are using a SCSI drive, there could be an issue with your SCSI controller (HBA) or the cable. Check and/or replace if possible. If replacement is not possible, you should be able to check the controller event logs and determine if there are any issues such as “device not ready” timeouts. If this is a SCSI drive, make SURE to UPDATE THE DRIVE FIRMWARE (I cannot emphasize this enough), as drives with older firmware may be subject to this type of issue.
There should also be an “0×0″ code (in the format 0×00000000, where “0″ can be any alphanumeric character) somewhere at or near the top of the BSOD: do you have that error code: Is it 0×00000050? If so, follow the procedure detailed here:
Additional troubleshooting steps can be found here:
Hope this helps