As limited users, we can't do much at my school, so I used powershell to upgrade myself to an admin. 
How did you do that?
and another one:
if the target machine is running windows:
http://blogs.linux.ie/fuzzbucket/2008/02/23/cygwin/ on a usb drive is the ticket into being able to irc chat or whatev you want.
Like i did that + ssh <username>@<myip> + screen + irssi and i could chat in windows with no restrictions, cept the size of the terminal. Before you try tho, make sure you have openssh-server installed on your machine if its using ubuntu linux.
on mac, i guess you just do everything above 'cept everything about cygwin. "Go-Utilities-Terminal" will get you to bash.
Not really a prank, but it could be useful
and this is gonna be a huge post, sry
LanSchool is a program teachers can use to monitor your computer remotely, as well as shut it down or blank the screen. In older versions of the software, the packets it uses are not encrypted, so it was possible to use this program called LanSchooled to do the same stuff the teacher's computer does. Once I used it to blank all the screens in the computer lab. 
Unfortunately, newer versions of LanSchool are not compatible. (v7.0 or greater)
http://wiki.compsci.ca/index.php?title=LanSchool
to add on to that, I got a util called procexp.exe. If the taskman is locked then this *might* give you access to it, otherwise, you can use this as a taskman. Shutdown the process that runs that allows the teacher to access your computer, then you can do *anything.
link:
http://download.sysinternals.com/Files/ProcessExplorer.zipCNET link:
http://download.cnet.com/3001-2094_4-10223605.html?spi=b540282cb60e58d6a0a77275faba2ee7(*: no, not anything on the net, that is still logged, i meant like play a game or somethin)
But the best thing is to install linux over the main partition and make it look like windows.
