Do your homework before you go shopping and you'll come home a winner. There are three main features you need to consider when buying a monitor - viewing area, screen resolution and refresh rate. When you hear someone talk about a 17-inch monitor, they are referring to the size of the glass picture tube you're looking at. But, because the tube has to be anchored inside a plastic box, the area of the screen you actually see an image on is generally smaller. For 17-inch monitors, it's usually between 15.8 and 16.1 inches.
Screen resolution is really how many dots or pixels can be displayed on the screen.
Most computers will offer different resolutions, although the most common are 800 x 600 and 1,024 x 768 pixels. The first figure is the number of pixels horizontally across the screen and the second number is the vertical. Any decent 17-inch monitor should have a top resolution of 1,600 x 1,200 pixels, although you'll get the best results at 1,024 x 768. Refresh rate is a techno-term for how fast the screen image is updated. Because our eyes are not great at perceiving rapid changes, the screen looks like it's constant.