You can re-record DRM protected videos using screen video capture software. That's what commercial DRM removal software does.

What file extension do your MPEG-4 videos have?

If you bought iTunes videos, not rented them, you can remove DRM protection with freeware Requiem. The latest version for Mac OS X is 1.8.17.

p.s. I think it is better to use a network media player than to burn DVDs from MPEG-4 videos. I don't really like Apple TV, but if you only buy videos from iTunes, it is probably the best choice.