Do they even have the name preceding the extension trademarked?
I may be wrong, but I don’t think they can do anything at all legal if they don’t. Also, if they ran out and got a trademark on it now, they’d have to prove it was trademarked before you registered it yours.
I don’t really know anything about this stuff myself. With all the extensions available now, it just does’t seem possible that, just because they registered the .com, they would assume any rights to the .net’s, .org’s or .whatever’s.
However, as Eyescoffee said; “I think there’s a difference between somebody like http://www.onlinecasino.com asking for the .net or .org domain, and http://www.yahoo.com asking for the .net or .org domain.”, it most likely makes a huge difference on exactly what .com domain name is involved here – whether it’s an unbranded, generic gambling portal or a well-known one.