I have found a wonderful alternative to the gym for me, a middle aged overweight granny with bad knees. John Walker, bless him, developed an exercise program for folks who need to start at the beginning. Bend and stretch, for instance, seems out of reach to some of us at the beginning. His program features levels of fitness....you start at level one and progress (hopefully) every week or so.

I'm sure to you exercise gurus it's too simplistic but for some of us who haven't strength or ability for anything but walking at the moment, it is a wonderful way to get started.

He has an online book called the Hacker's Diet which includes the fitness ladder. He encourages downloads and I would recommend the exercise program to beginners everywhere. Just a thought.
http://www.fourmilab.ch/hackdiet/