Curly, don't think about it and just do the following and I think you will get what you need. (Trust me in that users will not be admins or anything like that. What I am about to explain is exactly how it is setup here on dotnetnuke.com)

STEP 1: The module is placed on a tab. You then edit the module settings and assign Registered Users Edit Permissions to the module. (Just do it and trust me here, all situations below depend on this step being completed)

STEP 2: Once this is done, all you have left to do is configure each forum.

Public Forum No Restrictions: (All who can view module can post and view) If you want to allow registered users the ability to post or read a particular forum (we will call Forum A) all you have to do is make sure in Edit Forum that Authorized Edit Roles are clear, Is Private is unchecked, and Authorized Roles is clear. (THis allows registered users to view, post replies, start new threads in this forum)

Public Forum Post Restrictions: (All who can view module can view posts, but only those assigned authorized Edit can actually post here) In this case, if you want Registered Users to be able to post and you want Unregistered (ALL Users) to be able to view what needs to be done here is: Is Private checkbox unchecked, Authorized Roles left blank, Authorized Edit Roles having Registered Users assigned.

Private Forum: Select Is Private checkbox, assign authorized roles to view this forum. Control who posts here using Authorized Edit roles.