Can I install Vista 32-bit edition on one computer, and Vista 64-bit edition on another?
Windows Vista includes both a 32-bit installation DVD and a 64-bit installation DVD.
However, you may only install one or the other. Even though two DVD's are included, you may only have one copy of Windows Vista installed at a time.
If you upgrade your computer from a 32-bit computer to a 64-bit computer, then you may REPLACE your copy of Vista 32-bit with Vista 64-bit; however, you must never have more than one copy of Windows Vista installed at the same time, unless you purchase another copy of Windows Vista.