It depends on how the dvd is divided up. Some Dvds are decided up by Songs so all you have to do is rip one portion of it, but some aren't so you would have to rip the entire dvd. Programs like SimpleDivx and DvdFab are helpful with these kinds of things.
You will need a program called DVD Audio Extractor, it will rip any DVD karaokes in no time. You can pick any song you like before ripping (as long as there is a chapter on each song), then use Nero to compile and burn them onto a CD. Very simple, I do it all the times. Good luck!
PS: This is good only for AUDIO. For audio + video, you would need Super DVD Creator.