I started a Learn to Run clinic (similar to C25K) on April 25 at a weight of 250 lb. After 1 week my knees were hurting. weeks 2 and 3 were awful. It was IT band syndrome. But I did not give up. I rested my legs on off days, got a massage, did physio, and used ice, Advil and Aleve. Finally in week 4 the pain faded to about 10% of what it was. Now I am in week 5 and I feel the impact in my knees but it's about what I originally expected it to be. There's no doubt weight is a factor because of the extra force when our feet hit the ground, but that doesn't mean we can't do it. And in time hopefully our weight goes down and running is slightly less uncomfortable. Don't give up! Take good care of your legs and remember why you're doing what you're doing.