The creation of network bridge among two PC's networking cards in linux consist from a few following steps:
Prepare your interfaces:
ifconfig eth0 down ifconfig eth1 down ifconfig eth0 0.0.0.0 up ifconfig eth1 0.0.0.0 up
Create a bridge
brctl addbr br0
Connect network interface cards to the bridge
brctl addif br0 eth0 brctl addif br0 eth1
Turn on IPv4 routing
echo "1" > /proc/sys/net/ipv4/ip_forward
Turn off Spanning Tree protocol
brctl stp off
and finally start the bridge
ifconfig br0 up