There is still a lot of confusion about the difference between monitor size and monitor resolution. Put simply, a monitor's size is the physical dimensions which the screen covers--for instance, a 15" monitor (the most common) actually has about 13.8 inches, from corner to corner, of viewable space. A 17" monitor usually has about 16 inches of viewable space.
Resolution, on the other hand, measures the amount of visual information which is fit onto that screen. Resolution is measured in lines of resolution both horizontally and vertically. A large monitor can be set to a lower resolution, resulting in pictures, browser windows, text, etc. being blown up to a larger size--but reducing how much information can be seen, and reducing detail (giving a "pixelated" effect). A small monitor can usually be set to a higher resolution, which means you can fit more information on the screen, and it will be more detailed, but may be too small to be useful.
Monitors can be set to various resolutions, but the larger and higher quality the monitor, the higher the resoution can be set. Although some monitors can be set to as high as 1600x1200 pixels, about 90% of computer monitors are set to either 640x480, 800x600, or 1024x768 pixels.