[CentOS-virt] No module named cygvirtmod

I'm trying to set up a xen guest on a machine that already has a few others running (not set up by me). It fails with the following error:

+ virt-install -r 512 -n host5 -f /dev/vol0/lvol5 --nographics -p --os-type=linux --os-variant=rhel5 --accelerate -l http://bla -x ks=http://bla/ks.cfg -m MA:CA:DD:RE:SS Traceback (most recent call last): File "/usr/bin/virt-install", line 31, in ? import libvirt File "/usr/lib64/python2.4/site-packages/libvirt.py", line 12, in ? import cygvirtmod as libvirtmod ImportError: No module named cygvirtmod

This is a standard CentOS 5.4 x86_64 install, and I have not been able to find a solution on the web.