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MacTheRipper, RipIt or Fairmount for ripping/copying the DVD's content to your hard drive, but beware that one DVD takes up to 8GB of HDD space.

There is also Handbrake for encoding the DVD's content to a smaller .avi, .mo4 or .mkv file.

Use MRoogle to find lots and lots of thread about specific instructions about this, as this question is asked every second day or so.
 
I suggest Handbrake (which now also requires that you install VLC), so that you can compress down the video and save space on your hard drive.
 
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