Setting lower resolution on U2410

I just got a U2410 monitor and am viewing it at its native resolution of 1920x1200. My eyes aren't as sharp as they used to be, so I'd like to try it at a lower resolution, say 1680x1050 or 1440x900 but these options are not available in the Display Properties > Settings window. I'm running Windows XP Professional SP2, and I have installed the monitor driver from the disk. I don't like any of the non 15:10 resolutions as they distort the text.