I hear this all the time from non-running family & friends: I can't run, I have bad knees. I completely understand! I've been dealing with my injured foot for over a year now so I know it's no fun to do things that hurt!
However, it's not healthy to just not exercise at all! We all know this; we've been told since we're young. Get 30 minutes of exercise at least three times a week. So you can't run and maybe you can't walk either (I know my foot can get aggravated if I walk at too fast of a pace). What can you do then?
I have discovered Jessica Smith, a trainer who puts FREE videos on YouTube. She is peppy (not like Denise Austin peppy. Did one of her workouts last week -weird!) and has many low impact cardio workouts. Sometimes videos are not someone's thing but if you do these, you can find moves to incorporate in your own workout session.
I even love this chair workout from Smith. It's not the hardest workout I've ever done but it was good. And it's definitely better than nothing. You only get out what you put in (YOGOWYPI)! That's definitely true with exercise - you can workout as hard or as easy as you want.
I am a big advocate of exercise being able to change your life, but it has to start with desire. So go for it!