That is truly awful, and sad that jerks find the need to do something like that. That is one of the problems with a forum that is open to anyone. Who owns the site? If you are renting the URL from a company, contact them and have them delete the posts by accessing the HTML. If the problem presists, require people to register, and have their names be subject to admin regulations, or even see if someone could get admin privlages and regulate posts; kind of like a standard guestbook, where the owner can delete posts.
