Sadly this isn't as easy as you would hope. DVD movies are encoded using the MPEG2 standard which is completely different to AVI. Therefore, you need to convert (re-encode) your AVI's to MPEG2. Then, you need to author your DVD to create DVD video files which can include menus chapters etc.
An easier option might be to burn to VCD or SVCD. I know that Nero can take AVI's and burn then to VCD or SVCD easily.
If you really want to go to DVD, there are many products out there to help with the conversion and authoring - a google search will yield thousands
I use the free TMPGEnc
encoder to convert and then use TMPGEnc DVD Author
to author the DVD.
I know that other companies such as ULead
do many similar products (e.g. DVD MovieFactory
). Also, Pinnacle
are well known in this market.