Bad knees!

Ok, I CANNOT (at least I hope not lol) be the only one out there with this issue!! I just started the 30DS and I love how Jillian gives modifications, however, I don't want a modified jumping jack because I am overweight, I want one because 3 knee surgeries later, my knees just CAN'T take that kind of pressure!! Same with lunges!

I will continue to do her 30DS with my own modifications, however, I am wondering if there is an equivalent workout out there for me! I just don't feel like I get much of a workout if half the exercises I have to sit in a chair to do! And, while I agree strength training is important and burns calories, I also value the cardio.

I have begun taking stairs instead of the elevator at work (at least going up, coming down is too much stress on the knees, and that was the advice from a "fitness professional") but I get bored with the treadmill. Anyone have any thoughts? I do have a Wii, also Netflix, and cable. (just so you guys know what I have the ability to get/use!)

Thanks!