Together with the category system there is the /o/ handling for URL abstraction (in a way). Basic idea:
http://www.yoursite.com/o/12345 will display you the Object which has an ID of 12345. If this is a forum posting, the forum package would take care of the display.
Ask Timo or Dirk for details, search in the forums, as I know this has been discussed (somewhere). Or just follow Tom's advise ;).
