I think you either have the genetics to run or you don't. I lost about 30 pounds running and dieting. Went from 200 to 170. was about 37 at the time. Although in very good shape I could never get much over the four mile mark, or develop a pace much better than 10 minute mile.
My ambition was to run a half marathon. However, my left knee begin to develop pain after only one mile of running. In addition I had terrible ankle pain and went through bouts of faceitis (sp?). I tried different stretching, footwear and eventually sought out a physician who advised me to quit running. I now mix it up between eliptical and stair stepper. I miss the running, and it definately sheds more pounds, but if I even attempt a mile, my left knee feels like it's about to explode. I don't experience this pain even after 30 minutes on elliptical. I just hate being inside.
It seems to be horrible on your joints, so don't know if it's worth the gains.