If you "copied" via windows, your DVD is still encrypted. the best thing you can do now is to pretend to author a DVD in nero, but choose image burner. Then use something like daemon tools, or image ready and mount the image as a virtual drive.
Now you need to decrypt... but your in the domain of "ripping from stratch". Please read this topic:
http://forum.dead-donkey.com/viewtopic.php?t=4037