If you want to screw with someone, may I suggest getting a wireless USB keyboard, plugging the dongle into their computer, and typing while they are using the computer ;D We did that a lot for new people in my research lab. Lots of fun.
Also, if you know how, use the cron scheduler (for Windows or Linux) and have it open the CD drive every XX minutes. Thats pretty funny too XD
To do a remap, use the scancode map. This can be graphically edited using SharpKeys from RandyRants.com (at least that's where the details from the executable file link). I have changed other useless keys to something more useful.