Mac OS X 10.6+ GUI Tool for the Marble Blast Map2Dif and Map2Dif Plus converter scripts.

Instructions for Mac GUI tool (from HiGuy):

Simply open the application, and double click on a .map file. It will pop up a loading bar and convert the map. When it is finished, it will place the map in the same folder as the level.
The app will search for any images in the maps' folders or subfolders, so you don't need to have all your textures in the same folder as the .map. 

*DON'T* put the map somewhere with images of other things, like your photos directory, as this will waste space and time.
If you click on the app icon, it will pop up an open dialog. From there, you can select a map to convert.
You can also press Cmd-O. None of the menu items do anything useful, but you can always clicky clicky...