You can turn DVDs into DivX movies that will fit onto a normal 700mb CD. It is quite a complicated and lengthy process, and needs about 7Gb of free space on your hard drive. It copies all the information off the DVD, then compresses it down to a smaller size. The best program ive seen is called Gordion Knot. Goto:
http://gordianknot.sourceforge.net/
Download the required files, and use the guides there to help you through. Just to let you know, this is not particularly legitimate, although you could claim you are 'backing up' you collection!!