Just FYI, I pretty much have the setup suggested above (4gig of ram, q6660 quad-core cpu, 8800gt), and it works great. I geto 50+ fps everywhere.

You won't need two GPUs. You won't need Vista as long as you are OK with using horizontal-span for your two monitors. If you want to have it setup has two separate displays, yes, you'll need Vista.

I got my PC for $1000, without monitors.