Hi falko and cameron, I found the following on Skipfast blogspot which worked for me (Debian & LVM)
Recover XEN Guest Root Password
Have you come across a situation when you need to reset the root password of a XEN virtual box.
Logon Host machine run following command to boot guest OS in single usermode and simply recover root user password as normally we do.
#xm create -c /etc/xen/guest_vm_name extra=1