How can you burn mp4 movie files to DVD-R? Is there a format conversion necessary?

It depends upon your dvd player, but some can play mp4 files. You can use iTunes to burn the disk as an mp3 or data disk. If you use Toast, you can burn it as an audio disk which converts the files to dolby digital or pcm. I would recommend you experiment around using a dvd-rw. Then see how that plays in your dvd player.

Since it's a dvd-r you wouldn't be able to play it in a normal cd player. Only dvd player afaik.