I know that there is a conversion of my Photoshop atlas tutorial in French somewhere in the tutorial section. It is for Windows but the only real difficulty is just the keyboards shortcuts used, and those are quite easy. There might be a Gimp conversion of the same tutorial but it is not in French. So you could take both tutorials and sort of read along both of them at the same time. In the process you might be able to make the first French Mac Gimp conversion of my English Windows Photoshop atlas tutorial. Worth a shot at least, and welcome aboard.