From LedHed's Wiki
Ubuntu 10.04 LTS
Install
Within XenServer Create a new VM using the "Other Install Media". Make sure to enable OpenSSH either during the install or upon first boot. After the install is finished, boot the new VM. If you didn't enable SSH access during install, now is the time to do it:
sudo apt-get install openssh-server
Modifications
Files
Reference HowTo in PDF
Media:Ubuntu_10.04_XenServer_HowTo.pdf
XenServer Host Script for making a VM a PV.
Media:Makepv.sh