[libvirt] esx driver: XML format for guest OS type/variant

Hi, I am trying to create a VM using the Python bindings of Libvirt. I can successfully create VM from a XML template, but I can't find any way to define the guest OS type/variant like CentOS 5.5 64bit for my VM. The native format converted from XML is always guestOS="other-64" - which doesn't tell us much about the guest operating system. I have looked at the C libvirt source code a bit, and it seems like libvirt does not support defining guest os type using XML description yet. Is there any way I can set the guest OS type for my VM? Thanks, Jake