You make an iso filesystem with only the single archive file on it.

And if you mount the DVD it has the tar.gz (or bz2) on it.

tar zxf /media/dvd/backup01.tar.gz filename

Does the job just fine. Once the file is ON the DVD (after you create it and burn it to it) you just use it like any other backup media.

Remember you have to think of it like a tape. I've always written archive files to tape and not the tape device as it gets messy.

Of course this would also work on Windows in that way. BTW, all current GUI zip programs know and understand tar archives and also completely understand gzip files. Even in the Windows World. Heck even in W2K if you set a couple of registry entries, straight Windows explorer could traverse tar files and extract them from the .gz without add-ons.

But that is another story.

OSX shouldn't have *ANY* problem.