My son was diagnosed at 3 with pdd/nos and I remember it being a really frustrating time. Something was wrong, but they didn't know exactly what it was so it was pdd/nos. He is now considered as having "High Functioning Autism" or "Aspergers". One of the most helpful things we did was to take him off of dairy products for a while. It was extremely difficult as most of what he ate was dairy products. It made a huge difference in his behavior and he finally started building his vocabulary and started talking. We also used ABA therapy and TEACCH method therapy. The most helpful book I received was "Children with Autism: A Parent's Guide" Edited by Michael D. Powers, Psy.D. (keep in mind, I received this book when he was 3 and he is now 15) Fortunately we had many people to support us, not only family, but community and schools. That has not always been the case, as we move around a lot with the military, but we now find ourselves in a place where he is getting the care he needs. One of the most helpful things that I have done is to write an introductory letter to his teachers. I put his strenghts and weaknesses, behaviors, coping mechanisms, incentives he will work for, things to do and not to do for him, and a little about the disorder, and anything else I can think to put in. This way they are not left in the dark and my son is better off as well.
Hope this helps a little!