Mac files differ from PC files mainly because they have a 512 byte (if I recall) header added at the front of the file, that tells the Mac what kind of file it is, and what program runs it, stuff like that. There should be PC utilities (not Poser ones, general ones) if you look around for stripping these off. Mac Converter works fine, but only on a Mac, as noted. There is also a difference in how carrage returns are added to text files, too.