As far as windows goes, I'd probably say Vista or Win7. You said the possibility of a Microsoft interview is possible, so don't you think they would want you using one of their newer OS's and not being a vista hater?
Linux... personally, Ubuntu 8.10 has amazed me. Sure, it's dumbed down but there's no reason you can't fix it up and personalize it a little. I'd rather everything works out of the box, then pick and choose what I want to remove from there. That's just me, though.
Microsoft has a lot of different teams. Very few of them develop Vista or products that work exclusively with Vista. It probably won't matter in that regard.
That's definitely not the reason I didn't like 8.04. It was just way less stable than 7.10, and that was frustrating. I'll probably try Debian, and if I don't like it, I'll give 8.10 a try.
Warrior, the symptoms and system logs/monitors are not consistent with the other problems you listed. They'd definitely be reasonable if they were, but they're not. If they were contributing to the problem, there'd be obvious evidence. There's not.
If "fucking me over when I play WoW with graphics cranked" is using my memory to its fullest potential, then
DO NOT WANT.
I'm tempted to take out the memory I added and experiment.