as much as i prefer custom builds, you can still go for a pre-built system. some of them can be had for a great price, and there's a good bet that you can find one that will fit your needs.
since you're looking at a gaming computer, i would look for something like this:
that computer has some pretty high end stuff, and it still has the essentials: quad-core CPU, a DX 11 video card, Win 7 x64, and a massive hard drive. even if you did buy all the parts separate and then put it together yourself, it probably wouldn't save you all that much money to begin with.
hope that helps.
See the struggle of the faithless lot as they negate their time
How low to sink to the depths of their frame of mind