Thanks Jaygray that really helps me. I was actually looking at burning software. I would have to have Roxio Toast if I wanted to say back-up a DVD right?
I don't really do any DVD burning, so someone else jump in here, but I'm going to say, "not necessarily". Try this before you buy any software.
Open the Disk Utility (in applications folder or use spotlight to find it).
Insert your source DVD. Select New Image from the Disk Utility toolbar.
Select a destination on your hard drive. Allow Disk Utility to create the image file and save it to your hard drive.
Once it's finished, create a burn folder as described above, paste the image file into it and burn it to a new DVD.
The Mac image file (.dmg) is the equivilent of the Windows .iso file.
I'm not sure what happens if you try to burn copyrighted videos using this method. I've never tried. I assume their is some form of protection to prevent this though.