Have to have a motherboard, processor, bios, and software which support 64bit. Currently that is little if anything that can benefit from 64bit processing. I saw a test down with the same rig running 32bit os, and 64bit os, and there were some very minor differences in a few areas (rendering was one), but until software comes out to support it, it won't be a big thing.
If you have lots of money and want to be ahead of the game, then by all means start getting set up and ready. As for me, I'll wait until it's been out and proven for awhile, before I buy.