There are currently three variants available:
1. A vmware server tar-file
2. An ovf-image
3. A virtualbox image
Take the Virtualbox image.
1)Use VBoxManager clonehd .... to turn it into a raw image
2)Use qemu-img.... to turn it from raw into the type of image you want..
That what Ive just had to do this morning.. as we dont run either vmware or virtualbox..
although this works with RedHat KVM, it should work for XEN its essentially the same hypervisor.
Running quite well on an 8 Core Nehalem. :-)