Depends on what you want to do with them.
You can copy them to another DVD. In which case you will need,
DVD Decrypter or something similar.
Possibly DVD Shrink or something similiar if your movie is over 4.7 Gbs.
You can also encode your moive to fit onto a CD. You will need
DivX Codec or something similar.
Gordian Knot, Dr DivX, FlaskMPEG, DVDx or somthing similar.
A Bitrate Calculator.