What is a great program to burn AVI to DVD?

This probably has nothing to do with software and is instead all down to hardware. Basically, some DVD drives are more sensitive than others. When you burn a DVD at home, the grooves are not as deep as those on commercial DVDs (an over simplification, but that's the gist of it). Commercial DVD players sometimes are less sensitive than DVD burners and players that are found in PCs, and can be picky about what they'll play. This is mostly true of older DVD players. It might be cheaper and easier to spend $50 or so and buy your uncle a new DVD player.