Quick question on upgrading, opinions please.

My current set up is 2 x1gig sticks of ddr 400mhz ram, 7800gtx vid card, amd 4000+ 939, 450 watt power supply,x-fi platinum sound card. I wanted to do a huge upgrade for dx10, willing tospend upward of 2 grand. But seeing from the technology that coming out, im not sure if i should do that..My 2 choices would be this..either completely rebuild a new computer when vista comes out and transfer over my dvd drive, sound card, and hard drive. because im fine with all of those. and buy all new mother board , video card, power supply, and cpu(hoping for quad) the MAIN reason i use my computer for is gaming, specifically First person shooters. And my other choice would be to just upgrade to a socket 939 4800+ dual core , and a geforce 8800 768mg vid card. Obviously id save alot of money just switching out the vid card and processor, but for opinion sake, would it be worth switching to quad core 2 processor? thanks in advanced, jim