Well, my games box is a Shuttle SN41G2 (very small box) with the 9700, an athlon 2800, 1GB DDR 333, a PCI Nvidia Geforce4MX card, a combi dvd/cdrw drive and a 100GB maxtor HD. It gets quite warm on the case outer surface after it's been running for a while, but it's rock-solid stable, even when playing GTA3 or vice city, both of which are a little unstable in my view.

I would suggest that you have either a faulty card, or a faulty motherboard. I had one a while ago that would invariably crash after a few minutes of 3d gaming, no matter what card was used. The problem never occurred if the 3d was software generated, only when a 3d card was used. It seems to have been a chipset issue, as force cooling the chipset heatsink would delay the onset of the crash, although not eliminate it.

pca