Sounds like you are having the same issue's I've been battling Pez. Make sure you are using Orthos to stress test. I've PERSONALLY found OCCT to not work properly in Vista with NF4 chipsets.
Also...if your system is freezing, I would not suspect drivers. I would actually suspect your memory to be your weaklink. Drop the divider down another notch (from 166 to 133). That should help quite a bit.
Update for my rig:
I'm getting more and more stable by the day! I passed Orthos for 4.5 hours last night but errored out. I know, that's a bad thing.....right? WRONG! At least it didn't freeze during the test, or do a cold-reboot. So things are definitely getting better. If it doesn't pass for 12+ hours this time....I think 1333MHz HT Link may just be too high, so I may have to drop that idea
. I will of course, keep you all up to date