IMHO 64 is better. The good news is, if you buy the retail upgrade/full edition, you can get the 64-bit media from MS for shipping and handling ($10). The CD-Key will work with both flavors.
I plan do also use Vista64bit on a new gaming PC im building. This is just for new games, but have you guys played Painkiller and Farcry with Vista64bit? I have people telling me not to stick with Vista and to stay with XP. But I only want this only for gaming. What you guys think?
You could start by giving us some system specs to go by. However, if it is a recent system, you'll probably end up with 4 GB of memory sooner than later, barring another earthquake in Taiwan, so I'd just go x64 right away.