Is it a good thing to do hard cardio (Tae bo) for 10 to 15 minutes then switch to abs and legs on the floor, then do hard cardio (Tae bo) again for 15 minutes?

I had experience that once at a workout session and I have never experience that before in any of my exercise tapes. I just thought that might not be very beneficial.

Although this would be a pretty tough workout there is nothing physiologically wrong with doing bouts of cardio work interspersed with abdominal or even strength training. Actually, some quality research studies have been done that shows this type of training has the greatest impact on elevating resting metabolism levels. Having an elevated resting metabolism level means that you will be burning more calories even when you are sleeping!

The only thing you have to be careful with is having an elevated heart rate (from the cardio work) and then laying down on the floor to do your ab training. This makes it a little more difficult on your heart to push the blood around your body to supply oxygen to your muscles. Don't worry, you will not create any long term damage or anything. The only real negative thing is that you may become somewhat dizzy. Just remember to breath when you are doing your abdominal exercises. Many people forget to do this and if you are coming directly from a bout of cardio exercise it is imperative that you breath throughout your abdominal repetitions.