It was much different with us. Our dd was 4, she was sleeping in our room because she really had some problems with her room. She didn't start being in our room until she was 2 1/2, when we moved. But we let her pick out things, sheets, curtains, she had a curtain thing that went over her bed, like a princess...We made it into a really special thing. And then when we moved our youngest, it was because again, we had moved, and we couldn't fit the two beds in the room. But it was different because she got to sleep with sister. That was a big deal. Of course, she still comes into our room at night, slowly it is getting to not be until 5 or so, but there are still the occaisonal 230 comes into our room and wants to nurse all night. I know some people co sleep with more than 1 child, but I really don't think it is safe with my younger dd. She is about violent in her sleep. Kicks, lays on people, climbs all over. It is very important for me for her not to be in bed with a newborn.
But anyway, getting a little off. I would put the bed up, have him pick out sheets, maybe a new stuffy. Start with naps, if he still takes them. And sleep in there with him at first. And never say too much about sleeping there at night. Maybe every few nights say, would you like to go sleep in your new room? You can always come back here if you want to. Don't say anything about getting scared. Sometimes I think we put ideas in our kids heads. After awhile I am sure he will go to his room like it was his idea. It is an insanely slow transtion, but it was important for us that it wasn't tramatic. I don't want for it to back fire on us a month after the baby is born.