Forum Moderators: DixonJones
As you might imagine, KNOWING who sent it and PROVING who sent it are very different things. Unless there are real damages here, just move on. If it is your forum, block the user and the IP address the post came from.
There may be ways to track this person, but to do it with such proof that you will be allowed to collect damages - if in fact they can be proven in a court of law - will be time consuming, difficult, and very expensive. Unless this is just an overwhelming blow to your business or your reputation, I would just take steps to keep it from re-occuring (block the user, block the IP address, contact the IP administrator if that does not work) and move on.
Perhaps the best thing to do would be to consult with an attorney in your area who has experience in both the Internet and libel/slander issues. Then you can make an informed decision about whether or not you want to pursue this further - as opposed to one based on my advice :)