I've made a mxj external that can stream mp3s. It works OKish and you can check it out here:
But, it's probably pretty poorly coded and very inefficient, so I'm looking for some more experienced Java coders to help me out. Most of the work is done, it just needs some stream-lining.
So if anyone's interested in helping to add decent mp3 support to MSP once and for all, give me a shout!