I have a 8800GT and it's awesome.
I can play crysis on v. high but it is unplayable at resolutions higher than 800x600 (in my opinion).
Also if you decide to get a 8800GT bear in mind that the fan sucks and generate a large amount of noise.
I bought a zalman cooler to replace the old fan/cooler.
I also thought I destroyed the gpu processor when I washed it with alcohol. It was my first time replacing a gpu fan :S But it went fine.
Regarding ram, I am currently running 2x 1gb ddr2 bricks at 1066mhz (1.8v so it doesn't get too hot).
I've heard that you should buy enough ram to fill in for your processor L2 cache. For example if you have a processor with 12mb L2 cache, to optimize performance you need 2gigs of memory. But this was probably a false fact so forget I said it (I didn't follow this tip anyway).
Anyway with 2gig at 1066mhz you will do fine (even on Vista (but maybe that's just me)).