By default IPv4 packets are encapsulated on Ethernet subnets in Ethernet II or Ethernet DIX format in Windows server 2008/2003, Windows Vista/XP/2000. However, if you need to use IEEE 802.3 SNAP (Sub-Network Acces Protocol) then this can be done from Windows Registry.
The following procedure to edit the Windows Registry should help you disable the Media Sensing feature. This applies to Windows Server 2008, Windows Vista, Windows XP, Windows Server 2003 (if enabled) and Windows 2000.
1. Click Start - Search and type “regedit” (In Windows 2003/XP/2000, Start – Run). This launches the WIndow
2. In the registry, navigate to the following registry key
3. In the right pane, right-click and select New – DWORD (32-bit value) and set its name as “ArpUseEtherSNAP” and set its value as “1″. Setting “1″ will encapsulate IPv4 using IEEE 802.3 SNAP protocol in ethernet subnets. Should you like to change back to the default Ethernet II encapsulation at a later time, set this value to “0″ or simply delete the this key.