A common problem - here's Chris Pirillo on it:
"Poor Big John Midland. Every time he launches a Microsoft Office application the Windows Installer box comes up. Uninstalling and re-installing hasn’t helped the issue. Luckily, I have a very good idea what the problem is.
Most likely, a third party extension is causing this trouble. I asked John what version of Windows and Office he runs. He’s using Vista and Office 07. Both are still relatively new programs, and still have some bugs in them. He doesn’t recall installing anything new that would hook into Office. But that is probably the trouble here. I advised John to go through Microsoft Word and Outlook both to check active addins. Disable them one by one, and see if any of them fixes the problem. If not, then he needs to go through his programs, and uninstall or disable (one at a time again) any programs… such as Adobe Acrobat Professional… which tie into Office. I’d bet the farm that he will track down the problem through this method of madness."
And
here is a MS kb.
Put the message into Google for plenty more users with the problem. Looks like a bugfix from MS is required.
Good luck
