The VLC media player from VideoLAN is a free, open-source player that runs on Mac, UNIX, Windows and Linux. It can be used as both a media client and a media server, serving audio and/or video files to any size network -- public or private.
You can set up VLC to act as a media server using the built-in Streaming/Transcoding Wizard.
Download and install the VLC media player (videolan.org/vlc).
Start VLC. Select the "Streaming/Exporting Wizard" from the File menu.
Select "Stream to network" and click "Next."
Choose the location of the items you wish to stream. To stream from your iTunes library, for example, check the "Existing playlist item," expand the "My Music" directory, and select "iTunes." Click "Next."
Specify your streaming method. If you would like to stream online, select HTTP. Leave the "Destination" field blank and click "Next."
Check either the "Transcode video" or "Transcode audio" boxes to change compression rates and codecs for your stream. Leave them both blank if you don't want to change settings. Click "Next."
Choose an encapsulation format. Any of the possible formats will work for an audio stream. Click "Next."
Leave "Additional streaming options" blank and click "Next." Double-check your settings in the last window and click "Finish" to begin streaming your media source.