Native widescreen resolutions are not supported. To use custom resolutions go to...

Documents and Settings\*Your User Name*\Application Data\My Battle for Middle-earth Files\Options.ini
...and find...
Resolution = **** ****
...change **** to your desired resolution. You may need to enable hidden files and folders as viewable. This can be done from the "Folder Options" in the "Tools" menu by clicking on the "View" tab.