"How do I convert mswmm files to a Mac compatible file?"
mswmm files are the project format for Windows Movie Maker. The files tell Windows Movie Maker things about your video editing project like what video clips are used, which audio files you imported, which transitions go between which clips, and which effects are used. These files are essentially readable only in Windows Movie Maker and will definitely not work on a Mac. The two options for saving out a video file from Movie Maker are either DV-AVI or WMV. To create a Mac-compatible video file, open the mswmm file in Windows Movie Maker, save the movie at the highest quality setting WMV or preferably as a DV-AVI format file. Import this finished AVI or WMV file into iMovie or other Mac video editing application.