I'm running Vista Home Premium, 32-bit and have it updated completely using Microsoft Updates...including the virtual memory patch.
I've played hours upon hours of Halo2 since installing Vista three weeks ago.
I've also just this past week upgraded from an ATI X1950 Pro 256 MB DDR2 video card to a VisionTek HD2600 XT 512 MB DDR3 video card.
I have FIVE HDDs installed, one DVD-RW, 2 GB of OCZ PC6400 Dual Channel RAM installed and the OS is installed on a 160 GB Samsung SATA HDD. (Yes, my profile needs updating.

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Other games I've played:
Oblivion, Fighter's Stronghold;
The Witcher;
FlatOut 2;
Crysis MP and SP Demo;
BioShock Demo;
Call of Duty 4 Demo;
F.E.A.R. Perseus Mandate Demo;
and, others.
Looking at your system specs in your siggy, I'd take a good hard look at your PSU. Depending on the quality of that PSU....or lack thereof....that could be the very heart and soul of your problems with Vista.
Also, what kind of RAM timings are you trying to use? If you're running really tight timings on mixed bag RAM, you might be pushing too much. Loosen up the timings to see if things get better.
Have you also installed the motherboard chipset drivers for Vista?
Frankly, though, I would expect to have problems with a non-official copy of just about anything.