FreedomAudio is a free Open Source package that lets you stream MP3 and Ogg Vorbis files from your web site. It renders audio using a small Java plugin. The nice part about using a plugin is that you only have to download an install this once. Freedom Audio also now supports a plugin-free mode, but apparently this results in reduced fidelity.

Version 1.08 Build 20 shipped in April, 2003.

http://www.freedomaudio.com/