I just purchased a 19" LCD monitor to use with a 15" Powerbook. The item came with both DVI and VGA cables. The DVI cable does not fit the DVI port on my 2005 Apple Mac 15" powerbook. Is there an adapter I need? I assumed since the monitor had DVI and came with a cable I wouldn't need anything. The end of the cable is somewhat trapezoidal shape (as opposed to the port on the Powerbook which is rectangular). Thanks.