Hi,
- Create a role and assign it permissions to the Forum.
- Remove all other roles from the forum.
- Set the NotifyAdminsOnNewUserRegistration to True in the web.config (or user.config).
This will send you an email when a new user registers and if you want the new user to be able see the forum, you can add their account to the Role that has rights to the forum.
Hope this helps,
Joe D.