First, make a new template on your Dom0 xen host:
xe template-list name-label=”Ubuntu Lucid Lynx 10.04 (64-bit)” –minimal
xe vm-clone uuid=[UUID from step 1 here] new-name-label=”Ubuntu Precise Pangolin 12.04 (64-bit)”
xe template-param-set other-config:default_template=true other-config:debian-release=precise uuid=[UUID from step 2 here]
Create a new VM in XenCenter and choose the VM template you just created
Enter the following as install URL:
http://archive.ubuntu.net/ubuntu/
During Ubuntu Server install create a separate /boot partition with the size of 500Mb and set the type to ext3 as pygrub does not support ext4 very well.
After installation is complete, log in and make yourself root:
apt-get install linux-virtual linux-image-virtual linux-headers-virtual
apt-get remove linux-generic linux-headers-generic linux-image-generic
apt-get autoremove
cd /boot; rm *-generic
update-grub
mount /dev/xvdd /mnt
cd /mnt/Linux
dpkg -i *amd64.deb
reboot