Yes, Imax 3 is considered an HIIT workout. It's all step and there is no weights in the workout.There are ten step intervals in the workout each consisting of a low intensity step followed by a high intensity blast step. The blasts are very challenging and incorporate plyometrics. These workouts not only help you burn calories in the afterburn, they will also increase your cardio power, VO2 Max, and your leg strength. The actual name is a short form for Interval Max. Cathe's first full interval workout was called "Interval Max" and then when she came out with her following interval workouts she short formed them to "Imax 2" and "Imax 3". They are awesome and challenging interval workouts. If you haven't already, go to her "Shop Cathe" site and view the video clip on Imax 3 (her clips run about 7-10 minutes long) so you can get a taste of it. Enjoy!! Remember, you do not need to do more then 2 or 3 of these type of cardio workouts per week. Intersperse them with steady state cardio or circuits.
Just a tip, you might also want to try asking this in the "Video & DVD Questions…" forum as you may get more answers from other people.