So...
I installed XenServer 6.2. I installed OpenStack via DevStack (https://github.com/openstack-dev/devstack/blob/master/tools/xen/README.md). It successfully configured the OpenStack dashboard. I can launch new CirrOS instances.
But I have absolutely no idea how to fetch an Ubuntu PV image to use with it, and most of the tutorials I find out there seem outdated. I also tried to download cloud.ubuntu but I have no idea what format should I specify for the tar.gz file (and I somehow suspect it's not a PV image).
Help?