Do a search for the music.dat wherever you already have the game installed (i.e. C:/Nomad).
There will be a music.dat file there; it'll just be like a 2kb size file. It's a dummy file. Overwrite that dummy file with the larger, real music.dat file from the music addon. Simple as that.
This will work for whatever addons for whatever games. The music addon will be replacing a dummy file with the same name.
Well, unless the file format has been changed to decrease file size. In that case an installer is usually included.
That'd be my guess anyway.
Peace!