Here's what I found on wikipedia:
Tabata regimen[edit]
A version of HIIT was based on a 1996 study[7][8] by Professor Izumi Tabata (田畑 泉) et al. initially involving Olympic speedskaters,[9] uses 20 seconds of ultra-intense exercise (at an intensity of about 170% of VO2max) followed by 10 seconds of rest, repeated continuously for 4 minutes (8 cycles). The exercise was performed on a mechanically braked cycle ergometer. Tabata called this the IE1 protocol.[10] In the original study, athletes using this method trained 4 times per week, plus another day of steady-state training, and obtained gains similar to a group of athletes who did steady state training (70% VO2max) 5 times per week. The steady state group had a higher VO2max at the end (from 52 to 57 mL/(kg•min), but the Tabata group had started lower and gained more overall (from 48 to 55 mL/(kg•min). Also, only the Tabata group had gained anaerobic capacity benefits.
Strict tabata training is done to all out effort until you feel like you're dying or ready to puke or both--notice it says "about 170% of VO2max." Most trainers don't believe in working quite that hard, but it is important in any kind of HIIT (high intensity, interval training) that you bring your A game to every exercise. You want to perform the exercises with very high intensity. On a rate of perceived exertion scale, you would be at a level 9-10 with every exercise.
Because this form of exercise is so intense, it's important to let the body recover for a day or two after this type of workout. I suggest doing this type of workout 2 or 3 days a week max with a day or two in between.
On your off days, you can focus on strength training or lighter forms of cardio activity like walking or biking at a steady pace--more in the 7-8 range for strength training and a 4-6 range for other cardio activity going for a longer period of time. All of these types of training are important. They help to keep injuries down and your motivation up because you won't get bored.
If you want to learn more about tabata training visit TabataTraining.org.