You're using the old PrBoom 2.02, then. Check Readme.txt in the txts folder for the parameters to enable full screen mode and to change the screen resolution.
Use a batch file, shortcut or command prompt to add the parameters. They're added after the executable name.
For future reference it never hurts to open .cfg and .ini files in Notepad or something and look for relevant items like "Fullscreen 0". I know I can't really play a game running on an id engine without having to open the config in Notepad to set a few things not listed in the menus.
06-27-09 04:35 
