Hi J.! I'd like to chime in on the positive notes that the other moms have left. Kids absolutely DO take their cues from parents, so if you are positive and upbeat about the move, and truly enthusiastic, he will be, too. I would recommend giving him so extra time before, during and after the move to make sure that he knows that you're always there for him.
And, I think the best piece of advice I've ever read (even though I only have one child) is that when both children are crying, tend to your older one first. The baby won't know the difference, nor will she remember being "neglected" for a few minutes. Your son, however, may come to resent you always choosing his baby sister because she's younger and can't do anything for herself.
I hope everything works out for you, and I really hope you can pull a positive attitudue for him, and I hope he mirrors it back to you, to show you both what an awesome impact attitude can really have on life and happiness. :D