If it's a commercial disc you are trying to "back up" then you'll need to use a program to rip the files first. What are you wanting to leave out? Please provide more information about what you're trying to accomplish.
It is an already copied disc and what I want to leave out are some trailers and the copyright notice etc.
Rip the dvd back to your HD in file mode with Dvd Decrypter and then you can use Vobblanker to blank everything you don't want on the dvd. You can then re-burn the dvd with Imgburn.