The best tip i could give would be to buy WheyFX, a very good protein powder you mix with milk and its amazingly good. Not just taste but effect. I gained about 3-4kilos 1½ week muscle weight. Though I'm 200pounds~ and dont lose weight very easily :P Another tip would be to try out Creatine, that oughta help you gain some weight aswell. Theres Creatine that doesnt bind too much with water.