Sure do.. but first tell us all the privelages you have on those computers.. such as: are they running something like Novell Netware.. NetOpSchool.. and what can you do on the OS.. is it XP.. you kno.. just give more info.
i've got a trick for ya. click start> log off. besides expulsion you can get into serious trouble with authorities if you are cause doing something destructive.
ekÆsine is right. I play jokes on my computers on my home network all the time but your just asking for trouble if you mess with the schools computers.