Traditional Mac files (HFS & HFS+ filesystems) have TWO 4-byte codes identifying the CREATOR and the TYPE of the file. By default an OPEN FILE dialog will show files with compatible TYPE, but double-clicking a file will open the CREATOR. For example, you can have a JPG file that when double-clicked will open in Photoshop, another that will open in the QuickTime PictureViewer, and a third that will open in Internet Explorer. But they'll all appear in a dialog looking for JPG files. The Mac also has a File Exchange facility that knows how to map file types for PC files into CREATOR and TYPE codes, for files transported from other systems like PCs. But there aren't many file types set up by default, and most people don't bother. A PZ3 file moved to a Mac from a PC, for example, won't automatically open in Poser when double-clicked... but you can either use a utility to set the TYPE & CREATOR codes, or you should be able to set up the File Exchange control panel so that it knows a .pz3 file maps to Poser. (I'm not sure that'd help for a .cr2 file, though, since Poser searches them out directly. In fact, I've never tried to put a PC .cr2 file into the Poser runtime hierarchy to see whether Poser's search finds it without the CREATOR/TYPE data... perhaps it would, but MacConverter makes that irrelevant.) HFS/HFS+ files have two parts, a DATA fork and a RESOURCE fork. Control ("metadata") information about the file, including the CREATOR and TYPE, live in the RESOURCE fork. Applications can store arbitrary information in there, and Poser stores the preview image (.rsr on PCs) in there. Which means that even if Poser would find a "raw" PC .cr2, you'd get the generic non-preview without MacConverter. I don't know whether the Mac ProPack supports separate PNG data files for previews or whether it still requires the resource; but again, with MacConverter it really doesn't matter. Mac OS X is a bit different; while there's still HFS+ "under the covers", the system treats it as a UNIX UFS file system. But that's more relevant for Poser 5 than Poser 4; Poser 4 (and MacConverter) run only in Classic mode, which is a hosted Mac OS 9.2.2 running on top of Mac OS X... and it still uses the HFS+ filesystem with resource forks. I don't know what Poser 5 will use. It'd be nice if it uses a common file format across both platforms. But then, there are advantages to using OS-specific formats, too, and if there's any need I'm sure MacConverter will be there. So the only thing to watch for when trying to make Mac-friendly Poser downloads is to avoid those annoying and pointless PC .EXE installer packages. If you've just put the Poser files in a ZIP, you'll have no trouble.