I have two running KVM guests on an Ubuntu (Lucid) host. One of them uses the simplest NAT method, and DHCP inside. The other uses the bridge method and static IP inside. Both work fine. Can I mix the networking methods? I'd like to create some set of scripts which used the local 192.168.122.x address, no matter if the guest has or not has an additional bridged LAN interface. Having eth0 and eth1 interfaces inside would be fine. Thanks for your interest.
A simple configuration for a host which has both the virbr0 and br0 interfaces:
The interfaces file on the guest: