you completely failed to inform us what your present graphics card is.
Some older cards simply do not support wide screen format so a newer card is in order.
Generally speaking, if the graphics card has DVI using a DVI cable will allow proper wide screen format.
Just bought a Samsung SyncMaster P2350 monitor (23inch) and installed it. Have downloaded driver also. How do I get to use it full screen (or close to) without stretching the image? Do I need a new graphics card? - I am on Windows XP.