You aren't the only one who has been raising couch potatohood to an art form.
In the 4 months since I started this, I've rediscovered a whole bunch of muscles. Some of what I've found out:
1. I found the class in my local rec center to be like an aerobics class, and have gone to DVDs to learn what I need to know. My knees have no cartilage, and it's a challenge, but I like the centeredness and spirituality.
I use the AM and PM yoga DVD, and Rodney Yee does the morning section. Aside from being adorable, he does a good workout.
My husband gave me Yoga for the Young at Heart with Susan Winter Ward for my birthday -- I'm 55, and still over 90 lbs over where I want to be. The menopause workout is awesome. One thing that I really like about it is that, as the end of the workout, they summarize the alternate poses, showing how you can do interesting things even when you aren't real fit (like shoulder stands!)
2. Pilates is a stretching and toning workout. I love the feeling of it, but I studied dance for many years as a kid, and I do remember what it felt like. I'm so bad at it now, though! Still, every day I do get better, so this is a good thing.
3. Elliptical trainers are machines that you can work out on that put no strain on your knees -- which I need. Ask the instructors in the workout room of a health club which machines they recommend for you -- try all the different machines and see which ones you like. Then, you may be able to find a home version, if you wish to have a home exerciser.