I'm a little confused. You are downloading zip/rar files from the site and then should be extracting the game image from them. Once you have the image are you trying to extract from that? I say "image" because in most cases they are not "iso" files. They are usually cdi files, and I don't think you can extract data from them with an archive program. Unless you are trying to alter a game in some way (remove music, etc) you just need to burn the cdi image.
I have always been here