In vm.cfg of virtual machine check for this entry:
In the guest, edit the /boot/grub/menu.lst or /boot/grub/grub.conf with the following lines, add them somewhere above the first kernel entry, probably just below the default and timeout directives.
serial --unit=0 --speed=9600
terminal --timeout=5 serial console
Then, in the relevant GRUB entry add to the kernel line:
(append to the kernel line)
Reboot the guest and you should have the console. Now to check, you must attach the console to the guest from your dom0. This is done as follows:
# xm create -c vm.cfg