If your getting the 8800GTS then a X2 4600+ or upper end FX62 would be acceptable to drive it, if your going for the GTX then your holding yourself back...
why I say this is... I have a 7950GX2 that will clock upto the same speeds as a 8800GTX at stock in 3D Marks (11K in 06)... and a core 2 duo E6600.
with the E6600 @ 2.4gig and the 7950GX2 at stock speeds running the HL2: Lost Coast stress test I get 152FPS.
with the E6600 @ 3.0gig and the 7950GX2 at stock speeds I get about 160FPS.
with the E6600 @ 2.4gig and the 7950GX2 overclocked by 30% I get about 160FPS
with the E6600 @ 3.0gig and the 7950GX2 overclocked by 30% I get 210FPS.
and heres a pic from lost coast with most settings maxed out, FOV upped to get a wideangle picture... 66FPS with the core and GPU at stock speeds... I haven't been overclocking since I killed the first E6600 and motherboard.
http://aten-hosted.com/images/d2_lostcoast0004.jpg
hmm gonna have to look into that - I was getting 4x the fps of my old rig before... and this is what my old PC manages...
http://aten-hosted.com/images/d2_lostcoast0003.jpg
for comparison that is a P4 3gig with 2gig of OCZ Gold 2-2-2-5 and a gainward BLISS GF6800GTS Golden Sample 512Mb (BR02'd) against a 2.4gig conroe with 2gig G.Skill 6400HZ and a gainward BLISS 7950GX2...
EDIT2: with the core at 3.0gig and the 7950GX2 at +30% OC I get 100-120fps in that scene - hence where I was getting my 4x fps figure before...
with the stock cooler tho I'm not gonna run the conroe overclocked...