I stumbled around a bit before finding this solution. From some post:
- Quit all Office programs
- Delete these files:
- /Users/<user name>/Library/Preferences/Microsoft/Office 2008/Microsoft Office 2008 Settings.plist
- /Applications/Microsoft Office 2008/Office/OfficePID.plist
- Start any Office program
- Retype your name, company, and product key
It seems that, if you only delete one of them, it regenerates the other.