If you are on your own computer, during your own time (in other words with no class work to be doing), and not leeching school bandwidth, I'm not sure if they're legally allowed to confiscate your property. I'm fairly sure they aren't here, and if a student goes to the principal or dean on the matter, I'm sure they'll be forced to relent, or at least give your laptop back and just not allow you to use it in class.