I've made a media server (running on top of java 5 using the jetty http server and cyberlink upnp libs) that should work on windows mac and linux (not tested it on my linux box yet but I can get it working on the other two). It currently supports AAC,Ogg,Mp3,WMA (not lossless) and Flac (untested). It can also read the iTunes XML to build the song DB.
Its available under the GPL from
http://sourceforge.n...x360mediaserve/Its still a very very very early version but me and my friends have had no major problems streaming AAC, Oggs and MP3s to the 360. Its lacking any UI (other than a non compliant webform that allows you to add directories and iTunes files) and may require editing the transcoding scripts to do with the endianness of the platform you are using it on.
Great job, works fine on my iBook in OS X.