For a demo of Mserv's Icecast support, listen with xmms or Winamp to Mserv... playing Soundtracker mod files 24 hours a day courtesy of xmp, Ogg Vorbis and Icecast.
http://stormy.squish.net:8000/mserv.ogg (Ogg Vorbis 48kbps VBR).
You can also use the web client to see what's being played (bear in mind that there will be some lag depending on how much buffering your client does).
Note: I never managed to get Winamp 3 streaming Ogg files - if you have problems, you may want to fall back to the (better, more recent!) Winamp 2, which works great.