Well the first thing to do is to figure out what you want the computer to do. If its a gaming machine it helps to check out benchmarks of various things before buying parts. Generally for gaming the video card is more important than the CPU, but thats not to say you want something cheap. I will tell you that 495 is a pretty low budget for a "gaming system", but it really depends on your expectations. You're not going to play a game like Battlefield 3 in High settings on a high resolution on a $500 budget most likely.
Ideally $700-800 is a good budget for something that could seriously be called a gaming machine, and $1000 can seriously rival far more expensive pre-builds from companies like Dell/Alienware.