You didn't ask to back them up (despite the title of your post), you asked to convert them into a format you could play on a "regular" (set-top) DVD player. Burning iTMS music tracks as CD Audio is also not a backup, but it is a conversion that you have paid the right to do a limited number of times. This is all clearly spelled out in the iTunes EULA you agreed to. There's no criminal activity mentioned here, but the forum rules prohibit discussing violating EULAs despite their dubious legality.
To backup your purchases, copy the m4p (FairPlay DRM'd audio tracks), m4a (iTunes Plus non-DRM'd audio tracks), and m4v (iTunes video puchases) files from your iTunes directory onto a data CD or DVD using Finder's disk burning capability. In the event you should lose the data on your hard drive, you can recover them by copying the files back to your library from the disk (after re-authorizing your iTunes account). The data on that disk will not be playable on standalone CD or set-top DVD players.