Spoiler: Ninja has no idea what he's babling about. Vista is working perfectly for me after I installed service pack 1. I'm having absolutely no problems with Vista, that I didn't have with XP. The only decrease is the slightly slower managing.
Vista 64x, which is on my desktop computer (32 bit on my laptop), is running perfectly aswell, though I had a few problems with my graphicscard, and they'll persist until I get service pack 1 and perhaps some better cooling.
As far as program compatibility goes, I've not had any problems with that so far, except for a bit of confusion in 3D Studio Max and a few games. Once again, these were simply fixed by patching.
Vista is better than XP.
XP is more stable than Vista. For now.
That's the bottomline.

As for your computer, it's pretty good. I've got a 260GTX graphicscard, which is better than your's, but the rest of your computer looks better than mine. You didn't specify how powerful the quadcore processor were though. What you're looking for is Gigahertz and L1/L2 cache size, usually mentioned in MB, unless you're from the future.