First, Overlord needs certain files from the main VGAP program all in one directory in order to function correctly. If you are running HOST from it's own directory then you don't need to do anything further before using Overlord. If, however, you are running HOST using a path statement (for example: HOST game1) then you are going to need to copy some files into the game directory (game1, to continue to use the same example).
Copy the following from the main VGAP directory to the game
PLANET.NM, RACE.NM, STORM.NM, HULLSPEC.DAT, TRUEHULL.DAT
If you fail to copy these files, Overlord may either not work correctly or fail to function at all. The opening screen of the program, where you choose the subdirectory of the game you wish to edit, has a check box to indicate whether the necessary files are present.