Icecast is a streaming media server which currently supports Ogg Vorbis and MP3 audio streams. It can be used to create an Internet radio station or a privately running jukebox and many things in between. It is very versatile in that new formats can be added relatively easily and supports open standards for commuincation and interaction.
It comes well documented, however I would suggest the The Unofficial Icecast How To.
Listen in on my broadcast at: http://icecast.linuxweblog.com:8000/sandip.ogg.m3u