Is there a way to do that or do the maps need to be made from the original source to make a mac map? I dont have a windows machine and Im trying to wrap my head around this whole map thing as im a total newb trying to read and learn as much as i can.
I am not aware of any way to natively make garmin maps on the Mac. It might be that the mkgmap linux compiler also runs under OSX (which is BSD Unix).
Otherwise, you pretty much have to author the map on a Windows machine, then use Garmin's mapconverter software (which also runs on windows) to convert the file for the Mac.
I don't own a Mac, but don't they do Java? mkgmap is a Java compiler. JOSM is also Java. It's the standard OSM mapeditor.
Cool. I just "assumed" it was Linux. So that might work with Java on the Mac in that case. But still, it's going to be pretty tough to do any real mapmaking without a Windows machine.
Since the title of the thread was "convert an .exe to a Mac", I assume he is talking about a map installer for Windows that he downloaded here. The way to convert that to a Mac (assuming that the author has not already done so) is to use Garmin's mapconverter on a PC. If you don't have Windows and don't want to install it on your Mac, maybe you can use a friends machine to do the conversion, then put the file on a flash disk and load that on your Mac.
Download here: http://www8.garmin.com/support/download_details.jsp?id=3897
The biggest problem I've got with JOSM is that it doesn't seem as fast or as memory efficient as GPSmapedit. A small map in GPSmapedit takes a long time to load in JOSM. That said, there are guys making "cycle maps" with mkgmap, who are turning out stuff as snazzy as I can do with GM12.