http://madman.sourceforge.net/
I've been using this program for a few months now, called
madman. It is a very good music manager, handles thousands of files easily. Comes with a built in id3 tagger, a rating system, and what you would be most interested in would be the built-in http server.
I've connected a laptop to a stereo as a client, and contain the songs on a separate box. The music server box is a 700mhz machine, and the laptop is just an older 300mhz Compaq, both boxes are running Slackware-current.
The software is easy and quick to manage. You can shutdown the server, make changes with little effort. This makes it a very good program for those who have been unable to run some of the more complex streaming software.
Using NFS exports as mentioned is how I also make available a single DVD recorder to several machines.