colucix's idea was a good one.
Please try the following, when the DVD is in your drive:
find / -name nameofafileonyourDVD -print
You might as well do this as root, or you'll get a long list of "Permission denied" errors.
Wait until the command finishes (may take some time!)
Somewhere (hopefully in /dev/*) you should see the full path to your file, and thereby be able to access it.