My guess is that it will be 64 bit.  It just wouldn't make sense to me if they didn't plan on having something ready for Vista, and take advantage as quickly as possible to the 64 bit market.   MS already has a 64 bit OS, and I would think it was for developers to do some advance designing and programming in anticipation of Vista.

“Music is harmony, harmony is perfection, perfection is our dream, and our dream is heaven”
Henri Frederic Amiel