One last thing I can think of is those pesky 'VIA' 4in1 AGP drivers for the motherboard..check in your contol panel that you don't have any devices showing with a question mark.
It's a long shot but I've had unbearable choppy graphics performance twice because of some odd problem deciding to happen with this VIA stuff.
It's a long shot but I've had unbearable choppy graphics performance twice because of some odd problem deciding to happen with this VIA stuff.