Do a search in this forum for "looping". Make sure you search the archives too, since this question gets asked a lot. The initial responses explained how to make a clip loop using a crossfade "trick" that should work in any video editing app. There's also a tutorial on our website on how to do this trick using just particleIllusion, but that's not what you're looking for.
I'm not sure but I think we're being asked how to loop a DVD, not how to loop an emitter.
But like Alan said, Looping an emitter has been discussed at great length in this forum. I even cover how to do it with After Effects in my Creative Cow Master Series DVD, parricleIllusion Fusion Volume 1 - which you can find at http://wwww.creativecowtraining.net.
I've also explained it here at least a few times so take a look through the archives.