After disconnecting all the other drives, the install went off without a hitch. The computer booted into Win 7, took me through the first time user screens (adding the license code, setting up the username and password, and selecting the time zone, for instance) and took me to the main screen.
Win7 doesn’t see my mouse! And this is no trivial matter–it’s a MICROSOFT MOUSE! The same mouse that Win 7 saw throughout the upgrade process.
I chose “Add a Device” and the computer has been searching now for several minutes. I suspect a reboot is in order.