Good for you, starting is always the hardest part but once you get going I'm sure you'll really enjoy making exercise and good nutrition a permanent part of your life. It will seem like an uphill climb sometimes, but you get a real sense of pride after finishing a workout, at least I do.
So, in answer to your question about where to start, what kind of workouts do you like and what equipment do you have at home? (i.e., a step, free weights). Cathe's tapes are geared mainly towards advanced or intermediate exercisers but I think a lot of the tapes can be tailored to almost any fitness level if you know how, you just have to be careful and remember to follow your own guidelines and pace. Her step workouts are a blast and usually they're divided up into sections. Yo could start out just doing the warm up, first stepping section and then fast forwarding to the cool down. If you use just the 4" step to start and go slow, making sure you never get to the point of feeling breathless or dizzy, that might work. So you could enjoy Cathe's terrific workouts even as a beginner. Eliminating jumps and big arm movements will keep the intensity lower for you to get started, and then as your fitness level improves, you'd be able to add things on to make it harder (adding back in the jumps, etc).
I think even her Maximum Intensity Strength could work for a beginner if you start out with light weights to get your body used to a workout like that and gradually increase them over time. And if that's still too much, you can just do one or two sets instead of doing all of them.
These are just ways that I was thinking I'd alter the super-tough Cathe tapes if I were using them to start out. I think as long as you're careful, listen to your body and keep the ego out of it you can safely use them to get started.
I think Powermax is a great step tape; it has a long, thorough warmup and stretch, followed by 3 step sections. The first one seems almost ideal for adapting and using to start out. The 2nd and 3rd are long and tough, but again, just taking out big leaps and arms makes a big difference.
I LOVE Maximum Intensity Strength; it's a total body strength training program using free weights (barbell and dumbells, but to start out just dumbells would work, too). You could even break up the tape and do just the legs one day and the upper body the next, to get used to working out with weights (and go WAY lighter than they do.)
Those are my two favorites, but I believe that her older step tapes, Step Max, Step Heat, etc, might be more basic than her more recent stuff, too. Don't quote me on that, though!
So, as I always say, that's my two cents! Just make sure that whatever you do, you listen to your body, supplement those workouts with lots of water (not sodas, diet sodas or juice) and good nutrition. It's like the holy trinity of fitness, in my opinion. And have a good time! You should be smiling and enjoying your exercise, that's the key to making it a permanent part of your life, which it should be, right?
I'm sur you'll get LOADS of great advice from the rest of the gang, too. They're a terrific group. Welcome!
Lex