I want to have a baby but I don't want to tell my boyfriend?

Bad idea. The best relationships and families have open communication. If you are thinking of starting a family with your boyfriend, i strongly recommend bringing this up with him first.
No, that's wrong. First, that's a little hard to do - you need two to make a baby. Second, it's quite selfish to want a baby but not ask the father if he wants one before getting pregnant by him. After all, he would be the father - he has every right to be involved in the child's life. If he doesn't want anything to do with the baby but is willing to impregnate you, then you wouldn't have to hide it from him.