HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MRxSmb\Parameters -> New > DWORD Value -> 1 = off.
server side: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters -> New > DWORD Value (hex 0 for off?) - strange.
If using SMB2, not so easy: http://www.dataaccess.com/whitepapers/opportunlockingreadcaching.html