The following method has been tested on Ubuntu 12.04
KVM can be run in Bridged mode by making some changes to /etc/network/interfaces file and using the KVM command accordingly. Changes to /etc/network/interfaces file. The following changes will use the interface eth0 as Bridge interface.
auto lo iface lo inet loopback auto br0 iface br0 inet dhcp bridge_ports eth0 bridge_stp off bridge_maxwait 0 bridge_fd 0
The command to run the Virtual Machine in Bridge mode:
$ kvm -m 256 -drive /dev/sdb -net nic -net tap
