Even a nice 22" widescreen monitor costs $150-160 if you shop online.
My thread became a tech thread, something I'm actually good at.
If you're running a modern Windows iteration (Vista or 7,) the Display Properties options for a multi-monitor setup are fairly idiot-proof. Your monitors are numbered by Windows (it'll even pop a giant "1" and "2" up) so you can tell it which is on the right and which is on the left (or left-middle-right if you like immersive flight simulators. Or top-left, bottom-left, top-right, bottom-right if you're a day trader...) Laptops have been covered, most have an external display port that you can set to clone or extend the desktop. I can't speak to Macs, but I'm sure it's close to the same, except your second monitor is pearly white and costs twice what it should. (zing!
If you're going to get a second monitor for your desktop, make sure your video card has two ports. Most modern ones do, but not all onboard chips do. If you have an older or a cheaper PC, you might have to buy a second video card or forego dual monitors.