Setup xvm per Sun the most recent instructions. As appears latter Virt-Manager is broken in 126 ( vs 124), but this is not the worst thing supposed to happen. Virt-install rejects to install Fedora12 PV DomU which is not yet in the dictionary in meantime. XML startup file for f12 allows to avoid this restriction. I believe mostly connected with xVM version unable to handle ext4 FS for boot partition of Linux DomU