INT 10 U - VIDEO - DESQview 2.0x only - internal - GET ???
        AH = 81h
        DX = 4456h ('DV')
Return: ES = segment of DESQview data structure for video buffer
            BYTE ES:[0] = current window number in DV 2.0x
Note:   this function is probably meant for internal use only, due to the magic
          value required in DX