Right now, Im running an AMD Phenom II hexacore with 8 gigs of RAM and a geforce with another gig of dedicated RAM, on windows 7 64bit. Its pretty quick, alright.

But honestly.... you can get by with less. I did for years, actually, as I only upgraded to this system last year (my old system was only a single core on windows 32 bit - it lagged a lot... but it got the job done)