Question: I'm trying to use multiseat with Ubuntu, but I can't make this work.

I've read a lot of "how to", and the most of them are about doing a multiseat with some distro with GDM2, or KDM. But, I'm using the lightdm of Ubuntu.

So now I'm trying to make this multiseat with Xephyr, which I've already used to make a multiseat with the Debian 4 version. But I don't know how to call Xephyr in lightdm.conf.

Answer: 
try xrdp it will be the easiest solution. I installed vnc4server and then installed xrdp. and then I used rdesktop / tsclient / remmina to connect xrdp machine using IP Address.
There is a [wonderful blog](http://beforeafterx.blogspot.com/) detailing the process of getting an Xephyr based multiseat set up. He also is using Lightdm. Hope it helps.