Office 2003 prompts for reinstall

I checked Microsoft’s user groups and no one seemed to have an answer for this. I know the IT group where I used to work had to solve this one, but I can’t remember how they did it.

I installed Office 2003 on a new Vista machine, but every time I start Word I’m prompted to install the product. Hitting Cancel stops the process and opens Word correctly. So this is not deadly, just annoying.

Does this require a re-install or is it related to permissions somehow?