Ok, even though theres already been several posts like this I'll still recomend what I think is best for backing up DVD's.
First download MacTheRipper (this I feel is the fastest at backing up DVD's) of Version Tracker and use it to back up your DVD.
Once backed up compress with DVD2OneX (best for compressing DVD's IMO, good GUI, pretty quick to)
Once compressed to 4.4GB burn to DVD-R with Toast Titanium.
Out of all the methods I've used to back up my DVD's this is the fastest and my personal favourite, and I've backed up about 175 DVD's in total.
Or you could always use
Roxio's Popcorn , which incorporates all these steps into one program, but I've read reviews that its slower than other methods and apps.