I got [mt-daapd](http://www.mt-daapd.org) running on my Linux desktop where all my music files are. I found a [patch](http://hamadha.com/mt-daapd/mt-daapd-stable-avahi.diff) to make it work with [avahi](http://www.freedesktop.org/wiki/Software/Avahi) and [instruction and RPMs](http://www.terrysoucy.ca/index.php?/archives/17-More-Audio-Streaming-Goodness.html).
The only problem is that iTunes does not support streaming Ogg files. The [QuickTime Components](http://www.xiph.org/quicktime/) do a good job of local Ogg playing but I guess iTunes does its own thing with streaming. It is supposed to be possible to setup transcoding so the server streams WAV instead.
UPDATE: Only development snapshots of mt-daapd support transcoding. And they support FLAC. But they don’t support Avahi and the patch does apply cleanly.