Well eating is important, but eating will not help you gain muscle, only fat, unless you workout too. You have to make sure you are doing the right thing. It is a little harder to have sucess with gaining weight as a hardgainer. And sometimes working out too much is just as bad as not working out enough. I suggest doing mainly heavy squats, and heavy deadlifts. the only way to gain muscle is to give your body a reason to have the muscle. If you want to know exactly everything you need I suggest going to this
hardgainer site and read all the free articles, watch the videos, and sign up for the email class... then you will know exactly what you need to do.
good luck.
Cory