Free message board

Hi all,

I have a friend who would like to set up a message board where only invited members could view/post/start new topic.  He is part of an association of people spread over a great distance and is tired of the email clutter.  I found a few sites but some don’t have the restricted viewing.
Any suggestions?

Bigthumb, if he’s willing to pay for a domain name, I can help him set up a SMF board like HTMF’s.  He can make it so that only members can view and post.

Should only be $10 a year or so. 

They already have a website with a domain name.  Would that work?

Where is it hosted?  If their host supports php and mysql then it should work.