Ann,
I don't have a MAC but several co-workers do. In the past when having problems with Audio or Video files their solution has been to copy the files to the hard drive. Often using a windows machine to copy files to other media than onto their MAC
DVD drives are not completely stock yet so it might be that the DVD is +R and your machine will only read -R or the other way around.
My DVD burner can read both +r and -R but can only burn -R.
Since you can't get them to mount at all you might take a USB key and go to a friend's house that has Windows and copy the files a few at a time to a USB key drive.
You could also burn the files to a few CD-roms.
Patrick
