I say build it yourself. I mean you can get a better motherboard that will allow you more system management features. The processor isn't that expensive. RAM isn't expensive. The 8800GT's are pretty cheap right now. The DVD drives will cost you less than $30 per drive. Keyboard and mouse...well let's face it. Getting your own would be better because you can either go cheap and just get something that works or you can get any enthusiast keyboard you'd like.
All in all here's a breakdown.
Q6600 G0 Stepping:
eBay for $235 shipped but will come with an Intel backpack, OCZ thermal compound and 2 copies of Nero 7
ClubIt: $223.99 w/ free shipping
Newegg: Retail for $214.99 with free shipping.
Newegg: OEM for $199.99 with free shipping.
Motherboards: you will have to do your own research but I would put away at least $200-300 for one of the new P45 motherboards but ask around inside the Intel Motherboard area for reviews.
RAM: All Newegg for right now
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory - Retail CL5 $139.99 with free shipping.
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1000 (PC2 8000) Dual Channel Kit Desktop Memory - Retail for $89.99 with free shipping.
G.SKILL 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Retail for $94.99 CL4
PSU: Ask around again but leave aside about $150 for it
DVD Drives: About $30 a piece. You can usually find them on special on newegg with free shipping.
go to slickdeals.net and register and read the forums. You'll find pretty much every deal on graphics cards the day they come out. Set aside about $200 out for an 8800GT 512MB.
Case: Again that's on you but I'd go with a full tower case for better ventilation and cooling. Set aside about $200.
HSF: Everyone here loves the TRUE, OCZ Vendetta 2, Tuniq Tower but they are freaking huge and you have to buy your own fan for the TRUE and I think the TT as well but don't quote me on that. Anything aftermarket is better than stock though.
Hope that helps.