You need to either plane the boards to get the urethane off or sand the urethane off. The best solution is planing the wood. You could try some sanding to make the paint adhere better to the wood. Most paints don't go on very well over urethane. Sanding urethane is no easy task. Check out the local cabinet shops to see if they will plane the wood for you, many won't do it because the urethane is hard on their planer knives.
