I didn't start Cathe cardio until I'd already done Kathy Smith, Gin Miller and other beginner/intermediate-level workouts, and my first Cathe was Step in Motion III, which would probably be considered intermediate compared to her more recent workouts.
Before doing Cathe strength, I'd already done the Firm, Kathy Smith and several others.
It's possible to start with Power Hour (the nice thing about weight workouts is that you can change the intensity by changing the weights, or take a longer break between exercises, or--on DVD--skip segments if you need to), but it is a challenging workout! You might even need to do the squats and pliés with no weight to begin with, to get the form down. And definitely don't do the lunges the first few times out! Go light on weights and change 1/1 counts to 2/2 counts in the beginning.
For MIS(which is maybe a better place to start--it's an endurance workout as well, but not as intense IMO as Power Hour--but I have the hardest time with endurance. Ask me to lift heavy and I have no problem, but once I have to lift for more reps, I feel it much more!). Again, start with a light weight, or even no weight on leg exercises to get the form down. Don't make the mistake of trying to go as heavy as you can in the beginning: it's much more important, IMO (but, of course, this is ALL my opinion!) to develop excellent form, which will allow you to progress without injury.
Take breaks wherever you need to. You probably will need a longer break between segments than is allowed on the tape, so just let the DVD play in the background while you get in a few extra stretches, and when you feel ready (but not TOO long, as Cathe says, it's a break, not a vacation!), back chapter to the beginning of the segment.
You also might want to omit some of the sets of exercises. You can always build up to doing them all later (so you'll get a lot of mileage out of the workouts, because you'll be able to do more and more with time).
