I bet i know the solutions to your issue, and its not power. My roommate just got a 6600gt that didnt run to it potential and it was the chipset, im not sure which board he had but it was a via chipset, updating the dirvers helped a bunch but we (the computer nerds in the doorms) found that he needed to replace his board to get it to run @ speed, he ended up using a asus a7n8x-e deluxe inorder to get it to work. i hope this helps