The latest issue of Free Software Magazine has some instructions on how to install Mediatomb on a Ubuntu box. With Mediatomb you can stream your media to the PS3 using the UPnP protocol, which allows devices to connect seamlessly and simplifies sharing of media. If there is a compatible UPnP server on the network, the PS3 will automatically detect it.

The article can be found here: UPnP, Mediatomb, PS3, and me.