LambOfGod - He said he wanted a gaming pc
For the purposes of this post, I'm using newegg.com, but you might want to check around on some other sites.
Processor $315
http://www.newegg.com/Product/Product.asp?Item=N82E16819115003
Intel Core2Duo E6600
Everyone says this baby is awesome, and is highly overclockable.
Motherboard about $150
I don't think I know enough about motherboards to give you a good recommendation, but it has to be socket 775. I'd recommend DDR2 RAM compatibility, because that is going to be the new standard in a few months. Also IMO Asus makes excellent mobos
Graphics Card $319
There's currently a sweet deal on Newegg for the Geforce 7950GT which is basically the fastest graphics card out currently without linking 2 together. For gaming, you really do want to go all out on the graphics card.
http://www.newegg.com/Product/Product.asp?Item=N82E16814150189
RAM $215
2 GB of Corsair DDR2 667. You can't really go wrong with Corsair.
http://www.newegg.com/Product/Product.asp?Item=N82E16820145098
Power Supply about $75
It's really your preference, get one with at least 550 watts. Antec makes very nice ones.
Hard Drive about $100
It's really your preference here, the Western Digital Raptor is very fast, but is only 74 GB and is very expensive. I'd just get 1 250GB Hard drive for storage, but if you want you can by both.
You also have to buy a few more things:
a case
DVD Drive
network card? (if not integrated to the mobo)
cooling (fans)
We went a little over the budget, but this is a lightning quick PC. I assumed you didn't need a monitor, but if you do, get at least a 19" witha response time less than 16ms. If you need to make it cost less, get a different graphics card. I'd recommend this:
http://www.newegg.com/Product/Product.asp?Item=N82E16814143049