Starting with Windows XP, Microsoft has included a network bridging feature to virtually connect two different adapters or networks together. With a registry hack, you can disable Forwarding and/or spanning tree algorithm (STA).
Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Services\BridgeMP
Value Names: DisableForwarding, DisableSTA
DWORD Values: 0 = default, 1 = disable features
