"A few folks took Bill’s comments on Windows Server and applied them to Windows Client deriving that Windows Vista would be the last 32-bit operating system. That is an incorrect extension. While Windows Vista includes both 32-bit and 64-bit and there is a growing community of drivers for 64-bit Windows Vista we have not decided when Windows Client will follow Windows Server and become 64-bit only.
Read the rest here
There you have it, straight from the horses mouth.