to stream into SL you will need
1) a stream you can try your computer via winamp or you can go to http://shoutcast.serverroom.us/
which has good prices for stream uses.
2) a broadcaster this would be the shoutcast plug in for winamp or you can download other programs i would suggest if you want professional sound you get a copy of sam3 or sam4.
3) to stream into SL you need to give your stream url to the land owner that owns the land you want to stream on.
music you can get via your CD or what not.
thats all there is to it. note though you can try making your computer a server for streaming but you may be only able to channel a 24kbs or a 64kbs connection which is pretty crapy quality.