Just getting back to this, due to some testing with Ubuntu 13.04. Digging
through the errors shown in the ALT+F4 window, I finally found a launchpad
bug that pointed me towards this option (formatted for use in cobbler's
sample.seed):
d-i live-installer/net-image string http://
$http_server/cobbler/links/$distro_name/install/filesystem.squashfs
Using this, I am able to netboot 12.10 and 13.04 without hitting that
screen that says the "Install the System" step failed. Hope that helps you
guys out.