If you want a great single-click converter to turn your AVI's into DVD's, then download and install WinAVI at www.winavi.com
It looks like this:
1) The most important pre-conversion test is that the movie plays in Windows Media Player. If it doesn't, you'll need to go and get the necessary codec. (Use GSpot to identify the codec. Once you know what codec you want, the best place to get it is doom9.org)
2) In the WinAVI settings choose for constant video size (to fit a DVD).
3) Also setting the quality preference to "By speed" instead of "By quality" still produces great results!
4) WinAVI will create AUDIO_TS and VIDEO_TS directories. You only need the files in VIDEO_TS. Use these files to burn your DVD. (with Nero you just choose DVD Video mode and place all these files in Nero's VIDEO_TS folder)