Dang Buzkill, I had the same damm problem with my athlon. And i forgot what the hell i did. I think I made sure i had a 300 watt power supply, but there is a special program that sets your agp transfer rate to 1x. That is the key I believe. yes, I would try that first. I will look for it, but i dont think I have it anymore. My athlon puter shot craps and that is where it is.
it was the something something 4 in 1 drivers. maybe somebody can refresh my memory here.
Any way, you may have it already, just make sure your agp is set to 1x. Not 2x or 4x.