This one is the ULTIMATE practical joke, but takes some planning.
We had this guy at our office that would always go get our dinner (2nd shift). Well he isn't the most computer savy guy so it worked out better than we could have expected.
We downloaded and registered remote havoc from
here and installed the client software on his machine and set it up to run at startup. Then we installed the master software on both of our machines. This program is great, we started out with suttle things like opening the cd-rom drive, and playing tones. Then we started opening up porn sites on his machine. The greatest though was writing official sounding warnings and popping them up on his screen like "Windows has caused a fatal memory error in sector 7g and needs to be rebooted". This went on for a few hours, then I started writing them in spanish and german. The next day we were all standing around and the IT guy was working on someone elses machine, and this guy goes up to the IT guy and starts explaining his problem to him. I just about lost it when he told the IT guy about the spanish and german warnings.
