I decided to get Duke Nukem Manhattan Project today and its a great looking game for a game that was released in 2002. Of course there is one issue and that is that out of the box it doesn't support the selection of widescreen resolutions. Of course there is a way to solve the problem and its quite easy. Now this may work for other versions of the game but I did this using GOG so that is what I am using for this tutorial.
First your going to want to open the program. When the launcher opens check mark "skip this dialog next time". If you don't do this the game will save the settings selected from the launcher then of course you'll have to repeat the below step again.
Next step we gotta find the config.cfg file which by default should be located at "C:\Program Files (x86)\Duke Nukem - Manhattan Project\duke\base". Open config.cfg and once opened press and hold "ctrl" then press "f". Search for uset r_mode and press okay. Your going to want to change the following numbers from "640x480x32" to "1920x1080x32".
There you are finished that is it two steps that was easy right. So now all you have to do is open the game and the game will no longer open the launcher and launch in the resolution you requested in the config file. But remember do not go to the graphics options and change anything or it may go back to its defaults.
You can get Duke Nukem Manhattan Project from the following link: