CentOS virt - Mar 2012 - Installing Ubuntu 10.04 Lucid guest on Centos 5 using virt-manager

Hi,
i'm trying to install an Ubuntu Lucid PV guest on a Centos host but I
can't
seem to find a working installation URL. I tried
"http://ftp.ubuntu.com/ubuntu/dists/lucid/main/installer-amd64/" and
various subdirectories but I always get the error "Could not find an
installable distributio at ...". In the OS Variant box I chose Ubuntu 9.04
as that is the closest to what I'm trying to install.

Any idea how this works?

Regards,
  Dennis