I'm not sure that I've entirely understood your explanation - are you saying that the laptop screen and the external screen are showing two different images?
My (Vista) laptop (and most laptops that I've come across) has the ability to send its display to its own screen, to an external VGA screen, or to duplicate the display on both at the same time.
I can toggle between these choices with a keystroke combination. You may find that one of your function keys has a little diagram of a screen on it - this key, plus another (possibly CTRL, ALT or Fn) should toggle between the choices.
But the printer will print the same image, regardless of which screen it's displayed on.
I don't know whether that's of any help to you!