Okay, I think I'm starting to figure out what's going on. It may not have been a 32/64 bit issue at all. Lessons learned:
1. Windows 7 upgrade installers check to make sure you have an existing Windows installation before they will operate correctly. 2. If you don't have an existing installation, Windows 7 will "conveniently" indicate this by telling you your activation key is invalid. 3. My netbook had an existing Windows installation, but my MacBook didn't (not since I had the hard drive replaced). 4. Apparently, a previous failed attempt at installing Windows 7 counts as an existing installation...? (An installation of one of the pre-release versions of Windows 7 might count too.)
So the bottom line is that, even though you can't do an upgrade installation from Windows XP to Windows 7, you are required to have an installation of Windows XP (or Vista) to be able to install Windows 7 with an upgrade license.
Some users are referring to this as "punishment for people who didn't use Vista." It's almost as if Vista is inflicting one final hassle upon the world as it gasps its final breaths, never to be spoken of again.
-------------------- Chief iPod Correspondent
Senior Time Waster
Captain of the Planet Express
Assistant Jedi Librarian