Freezing Issues With Vista

[ndehmer]

Alright I made a small jump towards Vista a couple of weeks ago, and when it works, it is great. However the issue I am running into is that if I leave my computer sit for a random period of time, it just hard locks, no keyboard mouse and the display is frozen at what ever it was on. I can either hold the power button in for the 4 seconds, hit the reset button, or hit the master power switch on the PSU. I have installed all the Vista Updates, installed only the network and video drivers, and it still does it. I tried to do the "clean" boot option where it only starts the Microsoft process from the MSCONFIG utility. I don't know what to do. I don't think it is the system because I have two hard drives installed in the system. I have a 250gb with XP MCE2005 SP2 installed and works great 24x7. I have a 750gb with Vista 32bit Ultimate installed and it freezes up. I just move the power and SATA cable between the two to switch between OS's. I have tested the hard drive (brand new replacement seagate 750) with SeaTools, and it passes, as long as I keep moving the mouse or doing other things until the test completes. I also have run both the built in Memory Tester in Vista and Memtest and it past. I have reinstalled 3 or 4 times to no avail. I have turned off all Sleep/Power Savings options as well. The event log doesnt have anything in it other than the last shutdown was unexpected when I have to hard boot it.
Here are my specs
Abit AT8-32X Latest Bios
Opteron 180 at 12x243 (2916mhz) also tried it at stock
4x512mb corsair xms 3200 C2
1x3870 VisionTek or 2x1950pro Sapphire Ultimate
1x750gb Seagate Harddrive
Samsung DVD Writer
PP&C 750 Silencer PSU
D-Link DWA-552 Wireless Draft N card
all hooked up to a 37" Westy Monitor/TV running at 1920x1080

Any Thoughts? Right now I am running Xp again until I can get this resolved. My next step may be to get a new HD and try installing it on there and see if it still does it.

Thanks
Nathan