The best solution is to let Office Installer install what it wants to install, which should make the problem go away permanently.

If you can't do that (for example, you don't have the original Office CD-ROM nearby), Microsoft recommends that you use the registry editor (REGEDIT) to remove the following two keys from your registry:

HKEY_CLASSES_ROOT
   \CLSID
      \{438DA5E0-F171-11D0-984E-0000F80270F8}
         \InprocServer32
            \InprocServer32
               TriEditDocument Class

HKEY_CLASSES_ROOT
   \CLSID
      \{010E6CBE-FE2B-11D0-B079-006008058A0E}
         \InprocServer32
            \InprocServer32
               TriEditParse Class

from: http://www.fogcreek.com/CityDesk/kb/troubleshooting/MicrosoftOfficeInstallerR.html
see also: http://support.microsoft.com/default.aspx?scid=kb;EN-US;q304107