The Beastie Boys have released vocal only versions of several tracks for remixing. There does not appear to be any information about licensing. It does not get any more specific than this:

These A Cappellas are for your own personal use to make your own remixes.

I'm happy to see this, but it would be nice if they included some specifics about the licensing of the tracks, similar to how Interscope did when they released the GarageBand version of "The Hand That Feeds" by Nine Inch Nails.

Its safe to assume that if you do anything beyond making a remix and posting it to their web board, you would need a license. It would probably not be a good idea to make a remix or use the samples in anything that finds its way into a commercial release. Given the Beastie Boys heavy usage of sampling, I'd expect reasonable licensing options.

Put your Root Down and open up GarageBand..