I already responded in the other thread, but I'll explain what those files are. When I file is packaged like that, that means that the file is untouched by anyone except the person who ripped it. The advantage of this is that the images are error free and are pretty much guaranteed to work. Other images people could have used their shitty CD-rom drive to rip the game after they burned it putting a bunch of errors in the image in the process. The game might still work, but it will most likely take longer to load and put more wear and tear on your Dreamcast. For some reason 7zip sucks at extracting them, so just use WinRAR.