I agree with omega. Involve the your eldest son every step of the way. He'll be way more acceptable of the new child once he or she arrives. My oldest daughter used to "read" and sing to Mommy's tummy. It was her way of getting to know her little sister before she arrived. It'll be tough the first couple of weeks once the baby arrives. but your son will quickly adapt. If there is anything you want your son to do now before the baby comes, like give up a pacifier or be potty-trained, do it now. He'll see that you are preparing him to become a BIG boy and BIG brother. He'll feel special.