Right from the site that Mac Listed:
Processor and memory support
What about processor and memory support? Most Windows Vista product editions will be available in both 32-bit and 64-bit (x64) versions. Here's how the various versions support each processor type, and how much RAM they allow.
There's been some confusion about the difference between multiple processors and multiple processor cores (for example, both Intel and AMD are currently selling dual-core CPUs, and quad-core chips are on the way). While all of the Vista product editions support only one or two physical processors, none are limited to the number of processor cores they will support.