xscreensaveris a package you can find in your repository. It has all sorts of screensavers, including popular OS error screens. Install via Synaptic Package Manager, Adept, or what have you.
Good for confusing the hell out of a roommate, friend, or spouse, though I really don't recommend messing around with the desktop environment settings of a person who you may want to continue relations with.
For a temporary trick, try this Flash trick. The ESC key exits full screen mode in Flash.