Use SAM Broadcaster and Shoutcast/Icecast
SAM Broadcaster is not free, but you can always "buy" it (if you know what I mean...
)
You can add me at MSN for more details
By the way, you should have a good upload speed to support more listeners on a good quality.
You should go to
http://testmy.net (or any other site that can measure your upload speed) and take the smart upload speed test, and post the results here
/ 
