It should be. However, if for some reason Microsoft has 'invalidated' your key, then I don't believe you can use an upgrade key. Nevertheless, if you are sure it is merely because it's been installed/re-installed, then the upgrade version should be good!
Also, it shouldn't be an issue using
Backup and Restore as long as you burn a copy of the backup to a disk before you upgrade
. It is my guess, though, that you shouldn't even need to use it. If it is merely an upgrade within Vista and therefore shouldn't overwrite any of your files
.
Nick