Cheap gaming computer build. help

Hi i have around 600-700 $ to build my new computer but i don't know what components i need to play my games, the most intensive game i will probably play would be Far cry 2 or left 4 dead can someone give me a list of components i would need to build a fairly good computer with 600-700 dolors.
also i know how to build it i just need the list of parts.

thank you all

Here are some numbers:

http://www.hardwarecanucks.com/for [...] ew-16.html

See how one HD 4890 smokes Far Cry 2 - over 60 fps even at 1920x1200. It even beats the GTX 285 in some benchmarks

Left 4 Dead is less demanding, and you'll get ridiculous numbers like 90 fps.

I think the 650TX will do nicely after all, because with these games you will NOT need a second HD 4890. It's still powerful enough for two of those cards, in case some future game you like needs them. You'll just have to buy some $3 molex-PCI-E adapters for it if/when you want Crossfire.

spamalert

you can't buy 4770's anyway, so don't recommend them