eat light:

i haven't had too much trouble with my knees, other than occasional tendinitis from wanting to run too much mileage too soon. the key is to start with slow and short runs (some people recommend starting with run/walking, where you run for a minute, walk for four, run for a minute, walk for four, etc. and gradually build up to just running) and gradually work up the mileage. the problem is that your heart and lungs will get in shape faster than your legs. i would say the question of whether or not knee pain will go away with conditioning depends on what's causing the pain. if it's tendinitis the way to get rid of it is to stop running (you do something else to keep your cardio conditioning going, like riding a stationary bike or swimming) and do strengthening/stretching exercises for the muscle groups that are causing the problem. when the pain is gone, you start running again--slow and short.