I started as those "fat thin" boys. Weight about 150 lbs, all fat. Now I am 190, with ~8% body fat. I hear you are new at the whole bodybuilding, just remember to train smart not hard. IE if you eat right you will see much greater results than all the time you spend working out at a gym.
If you need help Training, Diet, and Muscle food boards are a great place to just sit back and read.