Are these AVIs stored on the computer or are they on a DVd already. Do you wish to burn these AVI files to a Dvd?
For backing up Dvds that you own, one option would be the link I will supply, all free. This would be for movies & not for episodic Dvds. Posts #67 to 74, but please also read post #78 & any questions that you have, ask here.
Movie only + 5.1
Unless you have a Dvd player that is capable of playing AVIs etc, you will first need to convert them into Dvd compliant files, IFO, BUP & VOB. This can be done with Dvd Flick or FAVC, there is even a free trial of a very good program, ConvertXtoDvd which I highly recommend. Then you can burn the result to a Dvd with ImgBurn, which you will come across in the above link.