Now let me have a good lookie here... As I'm Aussie, I find Newegg the easiest to use. Price match yourself if you can get stuff cheaper elsewhere, it's just to give you an idea. And a number of parts I chose below have manufacturer rebates - chase them up and you'll get a few dollars back.
Oh and also one thing, I won't be recommending wireless with 7 64-bit as I have been having issues with mine (used a number of different wireless adapters to test) and am using the ethernet cable for now - had to make some big changes to accomodate it.
Without further ado:
Front Case Fan $5.99
Graphics Card $66.99
Power Supply $49.99
Hard Drive $49.99
DVD Burner $25.99
Total = $510.91
You may think I'm disqualified because it's over, but take use of the manufacturer's rebates on some of the items and it will turn out under.
I await Ron's reply with baited breath. (And of course, any comments/questions jdawg183 may have)