Dang you never mentioned a montior, that eats up a ton of your budget. Sorry man a 500 gaming pc that includes a monitor isn't really gonna be a great gaming machine for very long. In light of this new info, I would suggest that you either:
A: try ebay to get a steal on some or a few pieces of this pc to save some dough, but quality will vary widely goin this route
OR
B: lower yourself into a last gen via chipset mobo and go with pc2700 or even pc2100 ram to save some cash. Goin pc2100 ram will also mean that you should probly end up with a 2400+ which is a decent chip, but not near what a 2500+ will do for you.
A: try ebay to get a steal on some or a few pieces of this pc to save some dough, but quality will vary widely goin this route
OR
B: lower yourself into a last gen via chipset mobo and go with pc2700 or even pc2100 ram to save some cash. Goin pc2100 ram will also mean that you should probly end up with a 2400+ which is a decent chip, but not near what a 2500+ will do for you.