Might want to fill out the form from the link in my signature. More info is always helpful.
Here's a preliminary build, assuming you don't need anything except the tower:
CPU/Mobo: X3 440 and Gigabyte GA-790XTA-UD4
$183 after rebate
RAM: G.Skill Eco 2x2 GB 1600 mhz CAS Latency 7
GPU/PSU: HD 5850 and XFX 650W
$335 after rebate
HDD: Samsung Spinpoint F3 1 TB
Case/Optical: Coolermaster 690 and cheap SATA DVD burner
Total: $766. Went a touch over.