Well ... you don't have to log in or register to visit most of the site.
Is the problem with the message that the bboard coughs up if you try to post and aren't logged in. That message is confusing, as it says "you can login as someone else if you want" after saying that this section of the bboard's restricted to members of a particular group or authorized users.
It should probably just go straight to the login page, and the wording on the login page could be improved, too, if necessary.
Would that solve it?
I kind of hate to put a login box on a site that's largely available to unregistered users ... it would seem to imply that you need to register to use the site.