Resolution issue

I go into the settings menu ingame, and when the dropdown menu for resolutions goes, all I see are 4 resolution choices (going up to 1440x900 (Widescreen), which is my Laptop monitor's resolution). I have an external monitor plugged into my Laptop which is 1680x1050.

Running WinXP w/ a 2.2 Intel dual core and Nvidia GeForce 8600GT.