Tom,

As j.drake suggests, a big mistake "many" people have is that the ISO is an "image" file, and not just a file... Coming from the World of Windows, I know that there is LOTS of file extensions, ICO, ISO, WAV, JPG, BMP, etc... too many to count, and whats worse, some of these extensions are for "specific" things, and still others, can be simply a data file.

ISO File Extension 101:
Actually, any time someone tells you the file is a "image", think of it like a ZIP file... The file can contain one, or more, files, packed inside, as is the case for ZIP, and so too, for ISO. Only differance is that the ISO file has a complete Operating System (OS), and all of its protections, file and directory structure, contained in it.

Have you ever copied a floppy disk? Do you only have one floppy drive? In most cases, you used an "image" for it. (or you had the option to use it) -=- If you want to "duplicate" a floppy, more than one time, you have the option to use an "image" of the Source floppy, to make additional Target floppies...

How this works:
When you duplicate a floppy, or any drives data (this includes a hard drive, or CD), it takes two devices to duplicate, one for the "input" and the other for the "output", in some cases, you only have one device, and its used for both processes. If both devices exist, like a CD reader and a CD writter, you would do a Disk-to-Disk copy, but when you want to make more than one, or you only have one device, this becomes a Disk-to-Image-to-Disk copy.

The "image" is a temporary file, used to hold the contents of the Source, or Input, and then can be used multiple times, to make the output, or Target -=- all without having to re-read the Source more than one time.

What people have done, as is the case with the ISO file, they saved the temporary file used to create the Target disk, and are distrubuting it to everyone. Using this "image" anyone can make the "exact" disk as the Source, without having the Source, or the file system, or the directory structure, or file permissions, or even the same Operating System, and it will turn out the same as if you had had the Source disk.

Hope this helps, if not for a little explaination,
Ms. Cuddles