Advice you not to get too deeply into gaming.
Colossal waste of money and time.
As opposed to spending it on 3D movies in the theater?
I remember buying 16MBs of RAM for my 486 for $300 (the RAM was of questionable origin ahem). Stuff will always be getting faster the second you buy it. I would spend some of the budget on stuff that doesn't change too often like keyboard, mouse and sound. Those 3 components are what you physically interact with.