You can check that the card will support the new monitor as follows:
Right-click on the desktop and choose Properties
Go to the settings tab, and click advanced
Go to the monitor tab and uncheck (hide modes that this monitor cannot display)
Click OK
Back at the Settings tab, see if you can select 1680 by 1050 DO NOT CLICK OK or APPLY!
Click cancel.
If you can select the required resolution, go ahead and buy the new monitor, then just repeat as above, but missing out the Advanced step, and clicking OK once you've selected the resolution.