I am using vBulletin 2.2.0 and I've been to other boards where "unregistered/not logged in" users cannot view *anything* on the board.....however they can click Register and sign up, then view the board and post...
I have changed User Group permissions in the Unregstered/Not Logged In section to all "OFF" (even VIEW BOARD=OFF) and it keeps everyone out however when they click on REGISTER it wont let them go there, it denies them.