Ad the adress to your forum bad word list so they will not get any links/traffic from you. Also if they host the images on their site, the images wont load this way. Secondly find out their MAC adresses and find the way to block it from your site.
go to http://www.whois.us/ and you will find their info by putting doain. maybe you could contact godaddy (they're hosted at ) to complain abuse also Domain Registration Date Tue Mar 18 01:58:55 GMT 2008 they're pretty brand new. I can just go ahead and submit abuse report now just curious how come you always stumble across all these new sites every time?
What forum software do you use? If it is vBulletin, place them in "Tachy goes to Coventry" Nobody else can see their posts but them.
It's under banning options and should be used only in extreme circumstances. The posts are not visible to regular users and staff have to click to see what was posted after seeing "admin thinks this member should be quiet for a while" (or words to that effect)
Someone from our abuses department sent an abuse email to the domain registrar - against my recommendation/permission.