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.