E6750 upgrade?

Well I use an E6750 @ 3.56Ghz, and still find it to be fine for all of the games.
RAM for you is an issue, when I upgraded from 2Gb to 4Gb I noticed better performance in Crysis Warhead - framerates were much more stable.
I would recommend a Radeon 5850 to replace your 8800GT - it is a good value upgrade (faster than a GTX285, and less money too), supports DX11.
I dont think you would need to upgrade your PSU to run a 5850.

Upgrading to 5770 will help too, but not as much as a 5850 would. Still, having 1Gb of VRAM instead of 512Mb will give you a noticable performance increase in many titles.

So yeah - if I were you I would upgrade in this order:

1 - Get a Radeon 5850
2 - Get more RAM. I wouldnt bother getting 2x2Gb all new RAM, but just get 2 more 1Gb DIMMS and stick 'em next you your existing RAM.
3 - forget about the PSU - see how you go with your current (I think the 8800GT uses more power or similar to a 5850, and the 5770 uses less than that!)
4 - see how you feel about getting a Quad Core at this point, I think you might find you dont need one!
5 - in the future get a new 1156, 1366 or similar mobo, new RAM and new CPU
6 - get another 5850/5770 and crossfire  

Just my 10c

(in short get 2x1Gb DIMMS + a Radeon 5850 and you will be rockin')

Wow ricky... looks like you need a haircut... LOL........... agree. The video card is "old and slow" and a couple of extra gigs of memory would help a lot. 4870/4890/gtx260-275/5850...maybe even a 5770..... without adding extra memory would be a good step up as far as playability goes......... you gotta have more v-ram..... 1gig or more depending on the game, especially at high res.

+1 to Ricky