If you ever turn on your computer and everything on your screen is too large, all you need to do is right click an empty spot on your screen, choose properties (personalize on Vista), and then settings. Adjust the bar that shows screen resolution (drag it right) until everything goes back to normal. On rare occasions you could run across the opposite where everything is too small. Then simply drag the same bar to the left. Here's what the screen should look like on XP: