That resolution is a bit low for a 20 inch monitor.Can't you adjust it using Display properties?
Agreed. Right click on your desktop and open properties/personalize and go to settings tab/display properties. This will show you what your current resolution is. If your monitor has been detected properly by the system, you should be able to move the slider all the way over to the right and that will be the max resolution your monitor will display. However, if it is some crazy high resolution like 2560x1600, then that probably isn't right. Let us know what that yields.
Also, I am assuming that you have an LCD monitor in a widescreen format. Is this correct or is it an older CRT?