For mp3 streaming, I'm using this:
www.gnump3d.org
It's written in perl, so you can get it working on almost every OS (I use linux). Easy configure, easy to use.
Streaming audio from an analogue source means that you have to encode it on the fly. Most probably you'd be able to do that with RealProducer and broadcast it, but it costs $$$.
I'd go with the mp3s...