To install xserver-xephyr just follow these instructions.
sudo apt-get install xserver-xephyr
Which will install xserver-xephyr and any other packages on which it depends.
|Maintainer||Debian X Strike Force <firstname.lastname@example.org>|
|Description||nested X server much like Xnest. It is based on the kdrive X server, and as a result it supports newer extensions than Xnest, including render and composite.|