Jeff, you may want to investigate cases where the user does not install NI software to the default directory. (James, did you do this?)
I got into some real difficulties by installing CVI 7.1 into a different folder than 6.0, and then later uninstalling 6.0. Specifically 7.1 went into ...\Program Files\NI\... and 6.0 was in ...\Program Files\National Instruments\...
Windows XP restore points saved me (!) by undoing the botched 6.0 uninstall, and I was able to then uninstall both in reverse order (7.1 then 6.0) and then re-install 7.1. Phew!
--Ian