Hi,
I just bought an AMD 4400+ x2 and 2 gig of mem, and got a geforce 7800GTX.. I also got a raptor drive (10,000rpm) but cos of cost i only got a 76gig (or 74gig, cant remeber which)...
Anyway, i've since played Rome:total war with pretty much everything maxxed out at 1240x1024.
Also HL2 with everything maxed out, but kept AA to x2 and anistropic filtering set to x4, seems smooth enough so could probably raise these.
Fear auto detected settings and put everything on max, i set a couple of things to medium to get a better fps, but there was no real change in how it looks, and it looks fantastic!
also while a game is playing you can alt and tab to desk top and then log on the internet to look at walk throughs etc... and i also have FoldingAtHome running perminantly in the back ground aswell as zonealarm security suite!
Oh yeah and oblivion looks ok but i had to run that at 1024x768 to get distance and grass on full with hdr on etc...
If i was you i'd maybe try get the 4400+ x2 for the extra money (and i hear they can be over clocked to 4600+ safely with stock air cooling only, although i'll not do that for atleast 1 year as there is no need to put the extra strain on it now). ((PLEASE CHECK FORUMS FOR OVERCLOCKING INFO BEFORE YOU DO ANY))
I'll be getting a bigger hardive soon, but probably just a 300gig 7200rpm one, as storage, and keep my mainly accessed stuff and high end games on my raptor)
Finaly, I'm sure that 2gig of mem must make a diffrence in games, but for all other stuff i think its overkill, only ever use about 1gig max when monitering usage through taskmanager.