Try relaxing your memory timings. If you are at 4,4,4,12 go to 5,5,5,15. MOBOs can be a little touchy when you increase RAM and this is often the fix. Don't know why the same problem is appearing under so many different configs. But try the relax anyway. There is no known bug using 4 gig in Vista (except for the install issue). You might try a different video card since that seems to be the only common component.
And I'd like to apologize for the anti-vista troll above - all he ever does in break up any Vista threads with his blind hatred. Totally ignores your actual problem. His sole mission in life seems to be hating Vista. Silly fool. LOL
Like notherdude says, relax your timings and maybe set yor voltage to factory spec's. I keep seeing this problem about memory and Vista. I quess I was just lucky with mine because I am running 4GB (4X1) Crucial Ballastic Tracer and have been since day one even when I installed Vista Ultimate 64bit I had 4GB installed and never had one problem with it, not even a hiccup. I will never go back to XP. Check my info on my setup and I've not had one problem.
relax your timings and maybe set yor voltage to factory spec's.
Yes. I forgot about the voltage! That Gskill is probably 2.1 v RAM (but check to be sure, it's on the label) your MOBOs are probably defaulting to 1.8v, that could be a common thread here too. We have seen many a flaky system stabilized by correcting vdimm lately.