Since you have a budget over 1300 you can get a very good rig. I found some parts that would be around 1300$ with shipping. No case, monitor, mouse, keyboard, speakers or OS.
AMD Athlon 64 X2 3700+
Asus A8N-E
Corsair XMS 1Gb (2x512Mb for Dual Channel setup)
XFX GeForce 7800GT
Antec Truepower II 550W
Creative Sound Blaster X-Fi XtremeMusic
2x
Seagate Barracuda 7200.9 300Gb SATA (to be used in RAID0, or so I would suggest)
Plextor 18X DVD±R Burner
Total: 1239$ excluding shipping in the price.
This is something I picked out for a guy on another forum. All parts can be changed, like you could change the HDD if you don't need that much, but usually people need alot of space on their HDD(s). The motherboard could be easily swapped for a A8N-SLI Premium or something in those lines but I've heard bad things about the A8N-SLI.