Running is good for your lungs, and heart, as it helps to build up your lung capacity. Smoking cigs is obviously bad for your lungs. If you only smoke "sometimes" I'd say stop now while you can. I smoked cigs for 15+ years and quitting was the hardest thing I've ever done. My lungs feel soooo much better though.

As for weed and your lungs, from most things that I read, weed doesn't have all the carcinogens that tobacco does. I still often wonder how good for your lungs it is though. Think of how gooey and resin coated a pipe gets over time. Wouldn't the same thing be happening to your lungs??