I tried out the tips and here are the results:

I have a Phoenix Bios with VERY limited setting options. No power management controls at all. It does have a memory test option though and I ran it for about 1/2 an hour with no problems found.

Interesting thing though, the computer does NOT reboot after 10 minutes when sitting in the Bios area (in other words without Vista running). So I'm thinking this almost certainly points to a software problem, rather than hardware.

Thanks,
Paul