If I go to forum settings all of my created forums are there, I went into one of them and visitors are there with the option of no access which must be what you are talking about. Thing is do I have to do this for each and every forum topic, I have 20 some topics options, and I would hate to have to do this to everyone one of them to see what the site looked like while not logged in.
If you do this to one of your forums, then access your site via another browser (if you normally use IE, use FireFox, or Opera) and then you will not be logged in. You can then see what affect your changes are having on your forum, without keep logging in and out.
