how can all users of a board be notified when a new topic is started?
By board do you mean just a particular board or do you mean the entire forum where if a topic is made anywhere, they will be notified? By default there isn't a way to have members automatically subscribed to receive notifications to new topics for a particular board.
Though you can try requesting this in mod requests (http://www.simplemachines.org/community/index.php?board=79.0). I can try looking into doing something like this, but I really don't know if I will be able to. ;)
Thanks very much for your reply.
My client has asked for 2 forums one for doctors and one for nurses. So I set up 2 boards in one forum and wanted to permit doctors and and nurses respectively. Then a major requirement was that when a question is posted on the boards, the respective member group would be informed that their help is required.
Hope this helps. thanks in advance.