Hi, Bob !
Well, if you want to increase lean muscle, you're going to have to start adding some strength training to your routine. Cardiovascular exercise is extremely important, but if you want to see some definition, you've got to hit the weights, do body weight exercises or use resistance bands. If you're not sure where to start, I'm going to recommend two books for you to find at either the library or your local bookstore.
The New Rules of Lifting OR Bill Phillips Body for Life.
Both are good beginner strength training books that will teach you the basics of strength training. You can also check out the Spark fitness section. Coach Nicole has some short 10-15 minute strength workouts you can try too.
If you've never used resistance bands, I highly recommend them. Join member SERGEANTMAJORs resistance band team. He's got a bunch of beginner to advanced workouts posted. www.sparkpeople.com/myspark/groups_individ
If you add some strength training to your cardiovascular workouts, you will see improvement with time. Also, there really isn't a difference as far as calorie burn between the treadmill and the elliptical. The difference for some people is that the elliptical is less stress on their knees and hip joints. You can do anything you'd like for cardiovascular exercise. you can take a daily walk, hike, take dance lessons, ride a bike, etc... it's all good.
So, check out the Sarge's team. I'm a member. He's got a lot of good info posted.