Are you wanting to just do a straight convert of the entire file or do you want to edit it and output that to DVD (MPEG-2)?
If you want to edit the video, you’ll need what is called a non-linear editor (NLE). There are many out there ranging in price from free to many thousands of dollars and all having varying levels of functionality and features.
On a PC, for free, Microsoft gives you MS Movie Maker which is not bad and has come a long way in the past couple of years. For under $100 there are a couple of good offerings from Sony, Adobe and others. Once you want some really advanced features you’ll need to move into the professional area where Sony Vegas Pro is about $500 (what I use and I believe the cheapest professional NLE) up to Avid Media Composer for about two grand, with others like Adobe Premiere Pro falling in the middle at about $800.
If you’re on a MAC you can use iMovie (which I think comes with it) or move up to Final Cut Express for about $200 or the pro version (Final Cut Studio) for about $1200.
