I love the Jillian Michael's DVDs, I bought them a while ago when she was still on Biggest Loser- the first one I got was Cardio Kickboxing- it's only 20 mins (25 including stretching) and it's literally nothing more than doing star jumps, imaginary skipping with a rope, some punching and some kicking, but OMG it's a workout, especially for your quads as you do most of it in a squat. I end up really sweating by the end of it, and I've been doing it regularly for the last few weeks.
I also bought a 4 pack, SHAPE UP by Jillian Michaels, and it's great as well, but you do need some handweights and they recommend having a step-up block thinggy as well. (When the get to the step-ups, I do star jumps or kicks or something)
I think you need to have some level of fitness before approaching these, as they are a definite workout- suggest renting them first and watching them all the way through so you can decide whether it's for you or not!