CGIcast is a selection of perl scripts which are intended to make it possible to perform live internet radio. Typically these accounts are about $5 a month compared with $15/month which you would pay to someone like live365.com to host your streams (and they still add advertising to your stream!).
There are 3 scripts - the client runs on your local machine and sends the mp3 data in chunks up to the receiver script running on the web host, this script stores the most recent audio on the filesystem. When the listener connects, they actually connect to the transmitter script - this serves the mp3 data from these files in almost real time.
Oh to make it work best you need to have some common unix tools - in particular SoX and "esdmon" are used for getting raw audio data. LAME is used for encoding audio to mp3, and cURL is used for pushing the data to the server (I could've done this in pure perl, but it saves about 15 lines of code).
You can also encode using OGG/Vorbis if you're wanting to get the best quality with the least amount of licensing problems. Oh and one example demonstrates relaying an audio stream from an SoX.