EVGA 7900GT KO
$289 (EVGA is the best GPU brand for Nvidia IMO)
$85.50 - $17 rebate (Patriot is good from my experience)
$74 (MSI is a really good motherboard brand)
Antec Truepower 2.0 550W
$90 (Antec is really good with their PSUs)
AMD X2 3800+
$84 (Western Digital is one of the best next to Seagate)
Total $919.50 w/o shipping
But you still need a case and a DVD drive. You can get a decent case for 60 bucks and a DVD ROM for around 20 dollars putting it at almost exactly $1000 w/o shipping. You may want to get a DVD burner but that will cost around $15-$20 more then the DVD ROM.
I decided to drop 2GB for 1GB so you can get a dual core CPU (1GB will play games fine anyways, even though 2GB will help in a few). You may need Windows XP unless you already have it (if you don't it will set you back 90 bucks).