For help with your running technique -- especially your perception that you're landing too heavily on your feet -- go to www.posetech.com and check our the Pose technique. Definitely light on the feet and especially good for beginning runners because they are not invested in "traditional" running technique, so it's easier to learn. You can run for a lifetime injury free with Pose.

Not to worry about running causing you more cardio stress than other things. The muscles used are different for various cardio training modalities, and depending on how you're using those muscles, and how efficiently you're moving, you can definitely have different results. My boggle is non-recumbent bikes. The way they work, they just whip my behind, no matter how well I can hit the recumbent bike, run, do real live biking, stairmaster, you name it. It's all in the leverage and muscle groups, so don't pay too much attention to it yet. Check out Pose, and keep up the good work!

Len