Wait so you're not building it from scratch, yet you need a hdd, ram, CPU, sli mobo, psu, graphics card, sound card, and other things like speakers? lmao that's building it from scrath dude. Only thing that isn't is the case which you might as well buy anyway. Anyway for a grand, you can get a pretty good comp setup to play you the newer stuff like Doom. I'd suggest something like:
This comes a little over 1000, but there's like 3 rebates which should put you under. Also the reason I put a 6800 GT instead of two 6600GT's is because why get two cards that use up your SLI capabilities and give you the better performance now, when you can get one card that is practically as powerful and cheaper and still leaves you that extra space for the extra card later when you want to upgrade? And that way you can have even better performance than the two 6600GT's. Just a wiser choice IMO and there's like a 50 dollar rebate on it too. I didn't suggets a HSF because you really don't need a special one unless you're OC'ing. The one that AMD gives you will do just fine, trust me. Overall I think this is a pretty good setup and will definitely give you good frames in Doom 3 and the likes. My system is almost identical and I get 135FPS in HL2 and CS: S, so you'll be fine with something like this.