64 bit procs can mess with bigger chuncks of data at a time, which certainly gives a perfomance boost, but only with a 64 bit OS and applications. You can still run 32 bit OSes and apps, though. 64 bit won't really be much of a benefit for a while longer anyways, so if you want Intel, take your pick, anything will do. But if you're in it for gaming and are willing to give AMD a shot, Athlon64 is an excellent choice.