Software :: Won't Unlock / Can't Find Settings To Reset Password

My mother works for a school district which provides laptop computers. They recently rolled over to newer computers and my mother purchased the old one from the school. Most everything works normally, although there are quite a few things(system preference e.t.c..) which require a admin name & password. It has been impossible for me to acquire these from the school and I am looking for a way to override these. I read on a forum to reinstall the hard drive from an operting cd. I have no cds whatsoever with the computer. Would love any suggestions on how to override thise system admin & password problem.