The stock heatsink Intel ships with their CPUs is perfectly adequate for anything you might throw at the CPU, so long as it's not overclocked. Running it flat out for a while it likely to get pretty noisy; if that's a concern, I'd suggest a somewhat beefier aftermarket heatsink.
Silverstone makes some average power supplies, and some fairly good ones, but I think
that particular one falls into former category. 400W should be plenty - I can't find the actual TDP of any of nVidia's 7-series cards, but the 7900GS won't be more than 150W (to meet PCI-E spec - 75W from the slot, another 75W from the 6 pin connector). Using a GTX560 as a point of comparison (as it has a TDP of exactly 150W), the system shouldn't break 320W under load
. All that said, I'd suggest paying the extra $7 for a 430W EarthWatts
I'm not sure why you'd bother with that video card at all, though, as another point. The 7900GS is pretty long in the tooth by now and I can't think of any particular reason to bother including it. If you need graphics performance, it would be worth it to get something new, as it's only just barely faster than integrated graphics are these days, and if you don't, it's awfully power hungry (and if it's anything like my 7900GT was, not particularly quiet) for no particular gain. I'd go with a more reasonable motherboard (do you really
need 3 16x PCI-E slots, dual GigE ports, and voltage check points?) like the Asrock Z68 Pro/Gen 3
(which will also support Ivy Bridge CPUs down the road if you want), and put the a bit savings either towards an i5-2500 and use the onboard graphics, or towards an actually modern video card.
I'm also surprised no one else mentioned the hard drive. "Green" drives as your primary system drive is a WTF-no sort of idea. 7200RPM drives are slow enough, there is no way in hell you want to use something even slower if you have any choice at all in the matter. Either go 7200RPM, or SSD+something.
And, apparently partially ninja'd