You need the original game data to use this, and most likely you will
need innoextract (available at SBO), in order to unpack it from the exe.
As an example, for the GOG edition of HOMM3, do this as a regular user:

$ vcmibuilder --gog /path/to/setup_homm3_complete_2.0.0.16.exe
$ vcmibuilder --convertMP3
