Need some workout//fitness info and nutrition/diet plan?

Im 5'11 and I weight 157, and my boy mass index is around the 18%-21% mark. I been working out and going to the gym but i feel as if im doing something wrong. I would like to drop my BMI to a good range and as well as i feel good about the way my body looks. I began thinking about this workout from this link (a href="http://www.topfatlosstrainer.com/2009/11/03/brad-pitt-fight-club-workout-diet-plan/)" rel="nofollow"http://www.topfatlosstrainer.com/2009/11…/a but obviously i need to drop my BMI to see results from this particular workout. What would be a good exercise/workout regime for me as well as diet plan to get my body back in order.