If you don't know what this game is then you must of been living in a cave for the last 14 years, DNF does support multi monitor resolutions natively without to many issues. Once again if your monitors width is larger then 1920 pixels and you have lots of bandwidth, set the quality to original and play the video in full screen for a much higher quality.
Direct Video Link: http://www.youtube.com/watch?v=pYldjJqg9dM
Channel Link: http://www.youtube.com/user/n11skid
Copy paste of video description:
Duke Nukem Forever on the PC, Original resolution was 5040x1050 aspect ratio of (48:10). If you are running a resolution with a width higher then 1920 (30'' monitor or multi monitor) set quality to original and view in fullscreen.
The video is from game launch, though one of the earlier levels. I've also put my usual annotations about how the game preforms with three screen.