Both P90X and P90 are excellent programs...but you can use either program. As Tony says through out all the DVD's "modify, modify, modify". There is even a guy with a prosthetic leg in one P90X DVD!
Everyone told me I couldn't do it because I am overweight. I have over a 100 pounds to lose, and I have multiple sclerosis...and I am doing the program with modifications!
Talk to your doctor first, he is OK with it...go for it and don't listen to anyone discourage you.