Comment 31 for bug 68440

Ok, I'm no Xen guy... however after experiencing a load of lock up's when booting the 8.04 Xen kernel (64bit) , destroying my fs by powering down by holding the button... I found this lame fix:

Now I can't speculate as to what is wrong, and I'm not going to... however try this (It also worked for ilowe in #ubuntu):

edit your /etc/X11/xorg.conf and force xorg to use Vesa driver.... reboot, at grub select your xen kernel... all being well, GDM should start

Section "Device"
        Identifier "Configured Video Device"
        Driver "vesa"
EndSection

Hope it helps (until somebody fixes the damn linux-xen kernels)...

FYI: If you have an nvidia card, change the line to

Driver "nv"

;-) nuff said