Something a little different, but might be interesting: the
SlimDevices folks have an open source audio server that has a pretty nice web interface that you can apply a number of "skins" to. The server itself is perl and I believe the latest version can use a mysql database for its library.
With the right skin applied, it could look pretty nice just using a web browser on your Z. Your laptop (or whatever your in-car computer turns out to be) would be the server and client to the SlimServer.
Or, if you want, the Zaurus can be a SlimServer client if you have mplayer on your Z to play an MP3 stream. If you don't have mplayer, you can try slimp3slave which is a tiny C app that mimics the protocol of a SlimDevices client and uses madplay or something similar to actually play the audio.
jason