Vista - setup runs whenever launching apps

I am running Vista Home Premium. Whenever I launch apps such as Word 2007
(Office Professional 2007) SP1 the setup runs as if it has never been
installed. Closing it and relaunching has the same effect even when not
logging off that user.

The same happens with other apps such as iTunes, although with iTunes it
never completes the setup, so what used to work is not inaccessible.

All is fine with the first user I set up, but nothing else, even when giving
them all administrator access.

Any ideas? This isn't good....

Thanks!

- Rich