Revit products released before Vista was released are not compatible with Vista.
The full list is here:
http://usa.autodesk.com/adsk/servlet/ps/item?siteID=123112&id=8991785&linkID=9243099
A search of the newsgroup shows that this question has been asked (and answered) before:
http://discussion.autodesk.com/thread.jspa?threadID=555053