All multicores are 64 bit last time I checked. Though as long as you don't buy a celeron I don't think it will really matter. The programmes will still kick your ass if that's what you're wondering. I'm not sure if there are any programmes optimized for quad cores (meaning if you buy one you might not get any performance increase from a dual core). Though I know at least chessmaster makes use of more than one core when it can.
Chessmaster 7 etc came out when there were only single cores at maximum 2 Ghz (and it still beat most humans without blinking) so why should the processor type matter now, really?
Can anyone tell me which is the fastest (all else equal) 64 bit or dual core (core 2?) processor for chess programs? Intel or AMD? I may buy a fast laptop for chess. Thanks