Ubuntu Jaunty 64-bit Kernel

Hi

Apologies if this question is a bit silly, I've only recently started working with Xen and am learning fast although still have a way to go.

I've installed the 9.04 system image from stacklet (Using pygrub) on a CentOS 5.3 Dom0 (Xen 3.0) and it works great, however I'd like to use the standard Ubuntu Kernel if possible, from what I understand 9.04's linux-image-virtual package comes with all the required modules to run as a XenU kernel. I run
apt-get install linux-image-virtual

to install the latest ubuntu virtual kernel (seems to install the vmlinuz-2.6.28-15-server image)
Then updated /boot/grub/menu.1st to be

### menu.1st ###
default=1
timeout=10
title vmlinuz-2.6.18.8-xenU
root (hd0,0)
kernel /boot/vmlinuz-2.6.18.8-xenU console=xvc0 root=/dev/sda1 ro
title vmlinuz-2.6.28-15-server
root (hd0,0)
kernel /boot/vmlinuz-2.6.28-15-server console=xvc0 root=/dev/sda1 ro
### /menu.1st ###

Upon booting, I get the grub menu, select the correct option and all I see is
# xm create ubuntu.9-04.x86-64.xen3.pygrub.cfg -c
Using config file "./ubuntu.9-04.x86-64.xen3.pygrub.cfg".
Started domain ubuntu.9-04.x86

I updated the menu.1st file to include the initrd too but exactly the same thing occurs

### menu.1st ###
default=1
timeout=10
title vmlinuz-2.6.18.8-xenU
root (hd0,0)
kernel /boot/vmlinuz-2.6.18.8-xenU console=xvc0 root=/dev/sda1 ro
title vmlinuz-2.6.28-15-server
root (hd0,0)
kernel /boot/vmlinuz-2.6.28-15-server console=xvc0 root=/dev/sda1 ro
initrd /boot/initrd.img-2.6.28-15-server
### /menu.1st ###

(The vmlinuz and initrd paths are correct, btw)

Am I barking up the wrong tree here? As Ubuntu's Kernel apparently supports XenU domains this should work as far as I'm aware?
Any help anyone can give to get this working or just to explain why this won't work would be much appreciated.

Regards