Not sure if this is expected or not, but I've been unable to boot a development guest kernel on a FC5 x86_64 host.
[root@hammer ~]# xm create -c fcdev-x86_64 Using config file "/etc/xen/fcdev-x86_64". Going to boot Fedora Core (2.6.16-1.2208_FC6xenU) kernel: /vmlinuz-2.6.16-1.2208_FC6xenU initrd: /initrd-2.6.16-1.2208_FC6xenU.img Started domain fcdev-x86_64 [root@hammer ~]#