I used the easiest method to gain administrative privileges on my school network. I wrote a small C++ program which looked like MS Access except asked for the administrator password and made it look like it wouldn't open until it was given. So one day when the headmistress is in the room I call her over and point out that I can't get into MS Access to do my work because it needs the password. She says "don't look then" and I look away, she enters it, and walks away. Then I just paste the contents of the clipboard and I have the administrator password. Easy.
The next year, it was changed, and they actually told me the password because they believed that I could get in anyway (since they found out I knew last year's password all year through). Fools.
This year they've changed it again (different management for the IT section) and haven't told me, but I don't need administrator access because all I need to do is ask my physics teacher to log in with his account when I need to do or install something (like the freaking graphics card drivers that they neglected to install).