I found this on http://www.freewebs.com/phobosx3/allresolutionsettings.htm

Maybe helpful to someone (:

"
This is how to get the higher resolution modes WITHOUT using the DFOptirun program.
Edit the DF2.CFG file and look for this line under //DISPLAY: Game_Res = (#)
These are the number representations:
1 is 320x240 mode
2 is 400x300 mode
3 is 512x384 mode
4 is 640x480 mode
5 is 800x600 mode
6 is 1024x768 mode
7 is 1280x960 mode
So to play in the 1024 mode the line would read like this:
Game_Res = 6
"