Theres absolutely no reason why a 2.8+gig dual core and an 8800GT (or even 8800GTS 640MB) couldn't play this game perfectly fine upto 1680x with good/high settings if it wasn't for the sloppy programming... if they ever actually patch it properly you wouldn't need a new GPU.
Indeed, I bet they never do patch it properly though. If it ever runs like MW2 online I'll eat my hat

All people can do in the meantime is use workarounds like disabling shadows or whatever works best, to minimise the problems.