if the song you want is part of the movie, then it is encoded along with the movie.
To remove the song from the movie you would have to decode the DVD (remove the encryption) and figure out where the song was located.
You might want to Google for that sort of program as help in decrypting DVD's is not in keeping with the CNET policies.
I have two CDs and 1 DVD Video. I would like to rip songs from each disc to make one CD that I can play in my car. I had no problems with the 2 CDs but the 1 song I want from the DVD Video won't rip. Can this be done. I have a Superdrive, OS X-Panther with i-tunes 6.0.2. up-to-date.