I'd like to offer software I found with a Google search for "DVD authoring free" and found DVD Flick.
Publisher's description of DVD Flick
From Dennis Meuwissen:
DVD Flick aims to be a simple but at the same time powerful DVD Authoring tool. It can take a number of video files stored on your computer and turn them into a DVD that will play back on your DVD player, Media Center or Home Cinema Set. You can add additional custom audio tracks, subtitles as well as a menu for easier navigation. The program supports over 45 file formats, over 60 video codecs and over 40 audio codecs. It's main target audience is people who know at least the basics about DVDs and video and audio files. This version is the first release on CNET Download.com.
And at Hack Attack:
by Adam Pash
Putting any old video file - like the DivX/Xvid-encoded videos you've downloaded with BitTorrent - onto a DVD to play on your TV can be a daunting task. There's plenty of software that tackles this sort of thing for a price, but as a lover of open source software, free's always my first choice. Luckily for all of us, authoring playable DVDs from just about any video file has gotten a lot easier in the open source community. This week I'm going to show you how to burn those downloaded TV shows to a DVD you can play in your living room using the free (as in speech), open source application,DVD Flick.
NOTE: DVD Flick's almost embarrassingly simple to use, but since it's a subject that can be confusing for people who haven't authored many DVD's, and it's a question we've been asked about several times before here at Lifehacker, we thought DVD Flick deserved a quick guide.
In a few simple steps, here's how to burn almost any video file on your computer to a playable DVD.