Windows Vista will ship in six editions.

All editions will be available in both 32-bit and 64-bit architectures, except Windows Vista Starter which will only be available for 32-bit architectures.

32-bit architectures can only run on x86 microprocessor architecture.

While, 64-bit architectures can only run on x64 microprocessor architecture.

I think there is no 86-bit architecture available in Windows Vista 'cause it's inpossible.