OK I found a solution as the package in the backports is broken (problem with python). You have to backport xen-3.3 on your own as according to this doc:
http://bderzhavets.wordpress.com/2008/11/03/attempt-of-prevu-xen-33-hypervisor-at-ubuntu-hardy-dom0-2624-21-xen/ -- libxen3 in hardy-backports breaks Xen 3.2 https://bugs.launchpad.net/bugs/297077 You received this bug notification because you are a member of Ubuntu Backports Testing Team, which is subscribed to Hardy Backports. -- ubuntu-backports mailing list [email protected] Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-backports
