What are you talking about?
Perhaps you mean that the Xbox360 can see music, videos etc that we stream from our upnp(MediaTomb) server in lmce.
And re kubuntu on the ps3. It won´t work with lmce unless you recompile the lmce parts you need for powerpc(Cell) architecture.
So far there have been some discussion about it noone have ever done a working PoC.
I forgot to add I don't think you need to install any software on the PS3 to use LinuxMCE, I think this because my X-BOX 360 was set-up doring the LinuxMCE install; It saw it and installed all the tools needed for Windows Media Center Extenders.