Motherboard - $120
GFX Card (Your 8800gt) - $230
Memoryx2 - $65 (Compatible with your mobo, low latency, and is the maximum speed supported by your mobo)
Processor - $239 (45nm technology on the wolfdale core, plus its a beefy 3.0ghz dual core for plenty of processing power)
Harddrive - $170 (10,000rpm to keep up with the processing power of your processor, plus its 150gb so its a good size)
PSU - $120 (610 watts and huge 12v rails, and is sli certified in case you decide to go sli with your motherboard in the future)
All that comes to $945. With that you get a high performance gfx card, two gb's of ram, a fast, big harddrive, a nice motherboard that supports sli, a sli-approved psu, and a very beefy processor.