are you sure it uses DivX? if you have Media Player Classic, you can check by clicking Properties. and also, .avi files are not only used to store DivX files but WMP, H.264, and many others.
i personally am not sure what Nero uses to parse and burn the .avi file to a DVD. if it uses VFW(Video for Windows), then ffdshow might be your best shot. if it uses a Codec, then ffdshow as well. or you could grab the official DivX codec from filehippo(although that one doesn't uninstall itself properly).
btw, to get ffdshow, go to
http://www.ffdshow.info