if you really have a 5-6K budget, then we need to talk. things to look at:
-Asus A8N32-SLI Deluxe (http://www.asus.com/products4.aspx?l1=3&l2=15&l3=148&model=382&modelmenu=1)
-(2x) XFX GeForce 7900 GTX (512MB onboard ram) in SLI mode
-A 1 kilo Watt power supply
-Athlon 64 X2 dual-core processor, either the 1MBx2 or 512KBx2 L2 cache
the list could go on. for 5-6K i could build you a dream system…