Want to set a subforum to require a password for guests, but not registered users
 

I've poked around in my settings and don't see an easy way to do this.

Basically, I'm making a community forum for a teacher's classroom. I don't want it fully public because they don't need everything to discussed regarding the class viewable by everyone else. Conversely, a lot of the parents may not be interested enough to register.

So, I thought I could password the site for the visitors and if only the parents had the password they could then view the info w/out having to register. Obviously, over time, if they got comfortable I would hope they'd register...

Also, I realize that there might be an argument that this just complicates things and that may/may not be true, but for now, I'd like any help/suggestions/codes to do what I'm asking.

Thanks! :)

edit: In expirementing with this I see that by default (somewhere) moderators and admins do not have PW requirements apply to them. Anyone have a hint where to find this in the admincp?