600-700 could be done might have to look around alittle but should be able to pick up a decent board, cpu, psu, case, memory,vid card, for close to that.
keep in mind cpu and vid card are going to be close to 400 just for the two, depend on the cpu.
price crunch go for the 9600 do you good, pick up a good board and 2 gigs of ram. (corsair, ocz, crucial, are all good nice case 400-500 watt power supply, should be set.
ECS 945P-A LGA 775 Intel 945P ATX Motherboard
Intel Core 2 Duo E6550 2.33GHz Processor
A-DATA 2GB (2 x 1GB) DDR2 800 Dual Channel RAM
Western Digital 160GB SATA 3.0Gb/s Hard Drive ( I might change it to a bigger one)
Sony CD/DVD-RW 18x Combo Drive
EVGA GeForce 8600GT 256MB PCI Express x16 Video Card
Thermaltake 430W Power Supply
Rosewill Black/ Silver Steel ATX Mid Tower Case