" how I can get the username of the user that made the last update" and "There is no "last updated by" column to use"
In version WSS V2, SPS 2003...functions/views should basically be the same in WSS v3 , MOSS 2007 discussion list
If your folks are logging into/securley accessign the site and or list...you can capture their respective info
I see a "posted by" column in the discussion type list. That gives the "posted by" which is the person/username who make the reply or new topic.
The last updated info is the modified column , again per a reply or a new topic created.
If you do not see these list items, you may need to change or "modify the view" to check those columns/items you are not seeing or create a new view and select the columns that you do want to see.
Hope this helps...
Scott C
WSS V2 and SPS 2003 with CorasWorks
Client Side Person..