what kind of budget are you on. the reason I ask is that this could range anywhere from $500 up to $3k-$4k depending on your budgett I can help you get the best parts for the money you have to spend
Perhaps this is the wrong section. At this point it belongs in hardware, i'll try to get a mod to move it to a much more active and appropriate section. Oh, and give jeremy a budget and he'll use it very well.
Motherboard
Memory/RAM (same thing)
CPU
Graphics Card
Hard Drive
CD Drive (optional but HIGHLY recommended)
Building your computer is not really that hard but will give you a lot of experience. If you wanted to, you could just buy the sam computer I made. It's pretty beast for gaming but I'm having some troubles with hard drive. I would say just go ahead and get a different hard drive than me. The whole rig cost me a little over $700. Of course you don't have to have a TV Tuner card, but I already had one so I put it in. As far as Windows 7, that will be quite a bit more.