I like the walking idea, I probably should have done that when I first started.
I was 340+ pounds and tried Taebo....that didn't work. I managed like 5 minutes! lol
Then I tried:
Women's Health: Perfect Body Workout and loved it. I still find it challenging. At first I could only get through like 7 minutes in the warm-up! Then I made it further and further. Now I can get all the way through the cardio segment, with cooldown, and I can do most of the strength and core training.
The women it in are not big, but they are different sizes and I love the fun and tone of it. I'm going to actually be getting more because I enjoy it so much. I believe the same series has a 10 minute workout or something short for people on the go.
When I started it was really tough. I also did Yoga and that did help me and I could only do like a few moments of that. Little by little I could go farther. Don't be intimidated by your body. My stomach was huge, bigger than it is now, and I couldn't bend very well at all. Only do as much as you can.