okay, so I've patched out the copy protection, easy.
I've created the hacked disk, as 1.44mb, then created it again as the correct 720kb.
BUT IT TURNS OUT THERE'S ONE MORE
That "DAT4" file? It's actually supposed to be to let you install this game to a hard drive, and it works by building signature of what your computer looks like (or as well as it can in DOS), and comparing it to a file.