Sort of. What I was actually suggesting was this
1. Tables are created which are identical to the post and topics tables, they could be called something like posttemp, topicstemp.
2. When posting as anything other than an admin or mod the posts will actually end up in the temp tables rather than the posts and topics tables. This could be done either by modifying post.php or, even easier, by having a new file called post_temp.php. That way the only alterations to punbb code would be to the destination of the "Post reply" and "Post new topic" links.
3. An admin plugin something like the mods multi-delete form would be constructed to allow for post approval.
4. When posts are approved the posts and topics databases would be updated in exactly the same way as they would be in the case of new posts.
5. Notification would be via something similar to the notification of new reports.
Doing it this way involves almost no editing of existing code. There is also no increased overhead because the "active" tables don't need new columns and the database queries don't need any further conditions attached to deal with posts that haven't been approved. This is a close a method as I could think of to make post approval a bolt on extra rather than a complicated mod.