I have nearly same system. e8400 but with a 4870 1 gig gpu. I'm not entirely up to speed anymore with nvidia hardware so don't know if yours is better or worse. I have 4 Gigs of ram but also a 64bit platform.
If you don't have a 64 bit OS then don't upgrade your RAM. Will be a waste of money if it isnt usuable by the OS.
I'm running the game pretty decent. I'm not using Anti-aliasing though and forests and buildings turned down. Rest is on high and a few on medium. I doubt I can run everything on high but thats the thrill
in 10 years time you can finally say YAY now i can run everthing on full with 100 fps :p