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Not much you can do if they are persistant. If you got his IP and can tell who's his ISP then you can send them the info. That kind of behavior is usually against the ISP's use agreement.
If they are smart enough to use one of the many proxy surf's out there, you can ban the ip's to those as they appear.
Maybe move to an admin view approval for newbs for a bit?
Dispelling the Mystical belief of Web Standards and tableless CSS.
Nobody gets excited about the tools used to build a house, people get excited about how the house looks and performs