You've already heard: a ".mov" file can't loop.
However, (as was mentioned by MTD) you can force the
playback of a QT file to "loop". Keyboard Shortcut: +L.
Further, I've realized that, once you've done that—set it to loop—and then you re-save the file, the next time you open that .mov file, it loops. Not only that, but if I move that same .mov over to my girlfriends Mac and they she plays it, it loops. So this feature can be saved into the file.
So, while we're here, on the topic of looping, we may as well exhaust it, right... You can post a QT file to the web and use proper embed tags to force it to loop.
In FCP, you can push control+L to loop your sequence.
And, finally, as was plainly demonstrated by Nick, you can force a DVD segment to loop too.
(Seamless looping was never mentioned here, and may be completely irrelevant for the application at hand. The precise implementation was never really mentioned so a "dirty" loop may be A-Okay! However, while we're on topic, it might be worth saying that a DVD loop will never be perfectly seamless. A looping QT file is basically seamless. Sometimes this is preferred: to not have a graphic with a visual hiccup. Most times: it won't matter. But with the DVD you'll certainly see the slight the stutter between the end and reset to the beginning. Even if you fade to, and up from, black—you'll see it. Again, this might be completely useless info. for the purpose specifically at hand.)