HoF Mod *does* come as a Windows installer. Not only that, but it includes a .dll file compiled using the Windows SDK (Software Developer Kit). No mods compiled using the Windows SDK will work with the Mac version of Civ4, so although we could no doubt get a Mac-installable version from the HoF staff, it would be of very little use.
The HoF Mod is compulsory for the HoF, so Mac players will not be able to compete. It's perhaps worth mentioning that, if we decide to support the HoF Mod for GOTM we shall either have to make it optional, and release two versions of each start file, or exclude Mac players.