intel doesnt have a 64 bit chip yet. . .
this thread discusses the intel duo 2 chips and intel duo 2 extreme, which are the portable and desktop versions of the 64 bit dual core chips. they are supposed to be shipping this summer. so as this thread says, the desktop version will probably be in the new PowerMac (or whatever those will be called) and hopefully the portable version will make its way into the mini, iMac, and MacBook Pros