@Edge, i'm glad you can rollback to the previous setup!
I don't use Xenserver, but Xen from the Debian repository and the setup is described here: http://www.howtoforge.com/virtualiza...an-lenny-amd64
I must be aware of several things as well as you can see here: http://www.debian.org/releases/stabl...l#xen-upgrades
It will take some time for me to find out how i can perform an upgrade in the best way. (Until now i only upgraded testing servers, but the xen environment is a little more complicated).