Delete the normal.dot after you uninstalled Office.
http://www.google.com/search?hl=en&q=thesaurus+stopped+working.+2003&btnG=Google+Search finds other ideas.
Was troubleshooting a pc for a client and the complaint was the thesaurus stopped working. Tried repairing and uninstalling and reinstalling to no avail.The spell checker and other functions of the program work fine. Another thing I noticed was that the windows installer tried to install components for word when the thesaurus was pulled up. Nevertheless, the thesaurus would not display any results.The OS is windows xp pro with SP2 but the office has not been updated from windows updates.