P.P.
Where is your son having his surgery? My son had an appendectomy at Children's Hospital in St. Paul. There was a resource person who was wonderful. She met with me and talked about the procedure and how to talk to my son about it. She also brought a bag of stuff the doctors would be using so that he could see them and she played with him, explaining what the things were and letting him use them on her. And she talked about how he may feel when he woke up and when he recovered. She was great.
You should call the hospital where he's having his surgery to see if they have a similar person. They could recommend some things you could do that are age appropriate.
Here is the website to information from Children's Hospital:
http://www.childrensmn.org/Surgery/index.asp
and here's a site with some books: http://www.medscape.com/viewarticle/525638_side1
Its hard seeing your child in the hospital, even with "routine" surgery. Find out what the hospital's procedures are for the parents. Children's Hospital let me stay with my son in the operating room until they administered the anesthesia. They let him stay in his jammies until he was asleep and put the back on before he woke up. It made it easier.
Good Luck and you'll be in my thoughts in the coming weeks for a successful and smooth surgery and recovery.