As everyone knows, divx/xvid is now supported on the PS3. And contrary to some inaccurate posts, UPnP streaming works fine. However, for Mediatomb, a popular streaming choice on Linux, a config file change is needed. The basics, as outlined in this support forum post, is to add to the config and then add files.
I got it too work for mpeg2 vids, but DiVX avi files and MP3 files show up as unsupported data.
(these same files work fine locally but will not stream for some reason)
I went with gmediaserver first, but may end up switching if this works better......