Assuming this is not concerning a copyright protected film, we can help here.
A free tool to convert avi to dvd-video is AVStoDVD. Works very well, and will allow you to make a menu if you want one. You can find it here: http://www.videohelp.com/tools/AVStoDVD I rate it above ConvertX because it can use the superior HCenc encoder. It is not as polished in the user interface as ConvertX, but it is free to use.
AVStoDVD can also use ImgBurn to automatically burn to a disk for you. I also recommend ImgBurn over Nero for most burning needs. ImgBurn is included with AVStoDVD, and is a free program. You can also download it and install it separately. www.imgburn.com