If your laptop already has a bulit-in wireless card, then you shouldn't need to buy a card for it. It depends what you mean by it having wireless built in though. That might mean it comes with a slot for a wireless card, or it could mean it has an internal wireless system, in which case it should be all set when you get an access point and router. I recommend wireless for the desktops too, because we used to have wires, and the house looked bad with blue wires going everywhere.

Its not as complicated as it sounds. Its pretty easy. You'll figure it out.