Let me try to be more clear here.
The forum I'm talking about is in a way like a guest book. There may be returning visitors, but there may also just be people who want to post once. In no case can a post be visible before we see it because it may be offensive (as happened once.)
So you go to a site, you read a few posts of other visitors on a particular subject (let's say tasting notes of wine) and you want o add yours.
What I am looking for would be a forum where registration is not mandatory (or very easy) but the main feature is that the posts do not appear until approved.
In my own forum, when a user "posts" all he is really doing is causing an email to be sent to me with a forum that contains his/her post. If I ignore thbis, nothing happens and n o database entry is made - very clean, you see? If I hit the submit button ont he forum, the post is ummm, posted on the forum with the info of the user.
I hope that clears it up. I'm not sure PunBB is something that will ever do this (it is a fine piece of work by the way) but it's helpful for me to kick the ideas around.