Welcome to the forums wimplewurm.
First off, please be aware that we do not discuss copyright protected material that is downloaded without permission of the copyright holders. Most downloads available on the net are not legal, but a few are, so we try to give people the benefit of a doubt here.
Second, there is no such thing as mpeg3 video. There are mpeg1, mpeg2 and mp4 files for video, and there is even mp3 audio, but mpeg3 video does not exist.
The most common mpeg format available these days is mpeg2. Mpeg2 is the codec used in dvd-video. Mp4 files can use a variety of codecs within them.
There are a couple of good, free conversion programs that will probably work for you: DVDFlick and AVStoDVD.
DVDFlick may be slightly easier to use for beginners, but I personally prefer AVStoDVD since I like the HC encoder that is included.