Im getting an external screen for my macbook pro, to have at my desktop to get a bit more space. Im looking at something from 20-24", but im really lot when it comes to the specs:S What things should I be looking for, like resolution, responsetime etc? And also, is it possible to have the screen like an extension to my mbps screen, som when I drag my mouse over one screen, when it hits the egde it goes over to the next screen?