Hi Paul and welcome to cdfreaks.
Short answer, you probably can't bkup to a SL dvd. If the file size is greater than approx 4300MB, you'll need more software. I know you didn't mean cd... ...I hope.
DVDFabdecrypter is not a transcoder, ie., it will not compress. You will need to burn to a DL disc or compress with another application. Shrink (freeware) will do this and do it well. You can also download the trial version of Fab platinum...free for 30 days. This will do just about anything you want and all within the same application. Apologize for the short answer...in a time crunch right now. Any questions, just post back, someone will help you.