get your lawyer involved... firstly how did you contact them? Just an email? What did it say?
Here are a few tips....
-First check there ToS to see if they are even to be held accountable to what people post... if they aren't it might be harder to get them to remove it since they aren't liable.
-Get your lawyer to write a cease and desist email demanding they remove it or you take legal action.
-Forget email and get on the phone with someone... I'm sure there are phone #'s on the yahoo site... if not a simple whois search of yahoo will give you a number to call to start with.
Hope this gives you a few tips on where to start
