I have been looking around for a project with similar specifications. If there is not one started I'd like to get some hacks together.
The concept is to have a headless box, that boots from the network file server and plays mp3s from the file server. The headless box will run httpd with php, be connected to the component stereo system. From various workstations in the house you can open a browser and connect to the livingroom_mp3.home.net and start and play the mp3s probably using xmms, or the command line version.
Please let me know if you have come by something like this and/or want to start a project.