Basically making bridge is rather straightforward. Just set the promiscuous mode on the bridged adapters (PacketSniffer sample shows how to do this) and repeat packets received from one bridge interface to all other bridged interfaces with NDIS_FLAGS_DONT_LOOPBACK | NDIS_FLAGS_SKIP_LOOPBACK set to avoid loopback packets. These flags combination will work for Windows 2000+, for earlier version you have to track MAC addresses and repeat packets according MAC address table.
