The notebook itself isn't a widescreen, so it doesn't display those modes. You can either return the monitor for one with a standard aspect ratio, or buy a new notebook with a widescreen panel, which should be able to drive the external monitor as you want it to.

Do you remember which ATI drivers you installed so that the 1680x1050 resolution is an option? I went through Dell's driver updates for 600m and installed the latest for the video - so now my Display settings are reporting driver as ATI v8.2. But still no 1680 x 1050 resolution. Went to ATI website and it does not list 9000 version under Mobility Radeon...but does list a driver for 9000 under just Radeon - which is called Catalyst Software Suite v6.11. I think I tried this as well without success. Would greatly appreciate if you remember what drivers you installed (and where you found) to get the 1680 x 1050 resolution option for attaching widescreen LCD monitor to 600 Inspiron notebook. Many thanks for your help, Matt