Xen, VLANs, and Load Balancing


I want to create a setup on XEN that has one or more machines load balancing for a number of other machines on a private network. This diagram shows roughly what I'm thinking:

Xen VLAN setup

The idea is that some machines will be connected to both the public network and the private LAN and other machines will only be connected to the VLAN. This offers some security benefits and reduces the number of public IP numbers I need.

The catch is I want to do this all virtually. Does anyone know of the recommended way to do this with XEN? I can't seem to find a HOWTO guide with this kind of setup. Pointers welcome.