[libvirt-users] Can't NAT in KVM

Good morning, list, I've been trying to get my KVM virtual machines to connect to the Interwebs for the last 3 hours with no success. I'm running Debian Wheezy (fully patched) and building virtual machines using KVM in Virt Manager. With the default, factory settings shown in virt manager, I have a default virtual network with the device name virbr0, which starts on boot and uses the default IPv4 subnets. I also have the default lo (loopback) network interface. I have tried creating a Windows 8 Release Preview machine and a Kubuntu Live CD machine. Despite recognising the hardware and network interface, neither machine will connect to the Internet. From what I can see in both virtual machines, it seems that neither is getting a DHCP lease from virbr0. I'm not sure what's broken or where to start looking for trouble because both the logs and the documentation are fairly sparse. Other possibly relevant information: I have a simple firewall configured with Firestarter in Wheezy. I use Network Manager to manage my only wireless connection to the world. I don't want to set up any fancy bridging or override /etc/interfaces because I only use virtual machines rarely but I rely on Network Manager to set up my laptop's networks so I don't have to. Any suggestions on how I can plug the v-machines to the web? With thanks, Borden