Just use the files from the mac version and throw an
update on it.
This is not the "official" way, but it works. Also on linux should you use that.
If you need some help getting the directory layout right, ask.
If you have the game only as a .dmg file, on windows you can unpack that with
7zip to get the game files.
EDIT: Regarding licensing, i can't really tell you. But since win/linux/mac versions came with the HiB and the humble store also has those (and you get all of them if you buy it), it should be fine imho.
Back in the days when there was DRM it was platform locked, but it's not anymore.