You don't want to run Prime95 for a HD6950 problem. You want to run Furmark to test the gpu and try using HWMonitor to view your temperatures, voltages and fan speeds.
Strangely, you didn't read everything. His computer is hard locking, not just graphically, but all over. So it isn't a graphical issue that is the root cause most likely. One thing unique to his system, two processors, chances are his chipset drivers are not updated, or something is causing a fatal error. Event viewer and stressing other parts of the system would be of benefit. Also note, he isn't having this issue when he just ran furmark, which further proves my statement.
I downloaded the file from Tyan for the chipset driver. I opened the file but i have no idea how to download the chipset driver. I ran the setup application but it said nothing of a chipset driver.
You built this computer last year, correct? The HD6950 is a new card then? What video card were you previously using? When you installed the HD6950 did you un-install the old drivers for the old card?