I agree with pat. On yesterdays ride, some rather large legged folk passed me up, but behold, 10 minutes later I was passing them on the hills. I was taking it easy, they were hanging on for dear life. I don't do any weight training, though I did do squats and lunges weightless during the winter to stay in shape.
My advice is the same as pat's: Spin, don't hammer, and it is not the end of the world if you have to walk, I did once on a particularly nasty hill, there's no shame in it.