I don't own STS. I think you might like 4DS better. Its a better choice if you have been away for awhile. You can customize the workouts easily. Its broken up into 4 days of workouts. Either you can do it as produced or use the premixes, which is what I do. I do the 'double cardio' premixes for a great (super fun!) cardio and then I do the upper body and the lower body on different days. You don't need as much equipment as STS. The program is only 80 (I think.) and its only a one week commitment. STS is a 3 to 6 month commitment. Also, keep in mind STS is designed to build muscle, this is not a weight loss/fat loss program. Some people do lose inches on it, some do not.
What happened with your knees? Do you think you might need one of those physical therapy dVDs designed to protect your knees? I can't really do hi-lo, it bothers my knees but running and step do not.
I don't know about you, but, I'm naturally very muscular and very pudgy. I put on muscle easily and I put on fat very easily. I do best with plenty of cardio, yoga and some weight work. In order to lose inches I have to cycle calories, carbs and eat fairly clean (some dark chocolate is ok for me.)
I hope some of this helps.
Alisha