You can try to get an older version of TMPGenc (freeware), before it became commercial. Also, there's a utlity called avi2dvd that bundles a number of freeware encoders into a single application, if you want to give that a shot.
In addition to the transcoding, you'll need a DVD authoring program (like TMPGenc DVD Author mentioned above). DVD Lab Pro has a trial version available; I fell in love with it, but couldn't justify purchasing it once the trial period expired. Since then I've been using various free alternatives, but none of them have matched in quality or ease of use. Download the free trial and give it a go; it's some powerful stuff.