Two major things are taking place in this process. First, the input file (avi) is being converted to a DVD spec mpeg2 file and the necessary files created to DVD format playback. Second, the output files are being burned to DVD.
Whenever you are having problems, you need to break down the various steps and find where your process is broken. Instead of having the software convert and burn directly to disc, have it create the video output files or an iso image. You can then test the output on the PC to see if it works. After it’s tested, you can then burn with various burning applications until you find one that works for you.
Nero is a decent burning application, but can suck a$$ when performing any other function. To convert avi to DVD, try ConvertXtoDVD (best choice - not free), DVD Flick or FAVC (last two are free). Have the programs create iso output files and then burn with ImgBurn (probably the best AND free burning app).