Hi Can you do me a favor?
Remove the nvidia video card and the drivers.
Connect the PC to you on-board card
Enable the On-board video in the BIOS
Install this chipset driver:
http://game.amd.com/us-en/drivers_ca.../integrated-xp
Reboot the PC and see what the CPU usage is.
See what errors are in the Device Manager.
Thanks,
Bill