Well, first off, the PC CD drives cannot read GD-ROM discs (That's what DC games are). So, if you're attempting to rip it using your PC, you're out of luck.
On that note, I will say that very specific models of CD drives can read GD-ROM discs, but require modification to do so (and it only works on certain games). And sorry, I have no idea which drives those would be. Search these forums though. It's been talked about multiple times.
If you're not using your PC CD drive to rip the games, and are actually doing it the "correct" way, I can't help you. And, to my understanding, it's against the rules for me to explain what the "correct" method is. Though, from what I understand, the setup is similar to ripping GC games, but I can't explain that either. Do some more searching (on these forums, or Google) and I bet you'll find more information. Mouser X over and out.