The $500 range for computers is pretty epic right now.
You can get a 9800GT for $130 or less if you shop around
There's plenty of options for CPUs ranging from $80-$180 for budget systems, I'd personally take a look at the E7200 or E7300. They really offer amazing performance/price. And I believe the E7200 is $150 or so.
mobo you can probably get for under $100 if you don't want to plan for future upgrades or overclocking.
Memory ehh there's tons of deals floating around for 2gb or so.
As for psu drop in some sort of 420w corsair or equivalent.
HDD your choice
Happy Computing!
edit* holy fuck me I just spotted this board:
http://www.ncix.com/products/index.p...nufacture=ASUS
That's one fucking sick ass I/O I might buy this tomorrow for a media pc lol....