Do you still have your video resolution set to the same as you had for your 15" monitor? If it's still set to something like 800x600 or 1024x768 resolution, you'll get the effect.
If the monitor's native resolution 1680x1050 isn't present in the resolutions list to choose from, you probably still need to install a driver from the CD that should have been supplied with the new monitor.
If you're not accustomed to adjusting video resolution, right-click on the desktop and select Properties, then the Settings tab.
Edited by Platypus, 22 October 2007 - 06:56 AM.