Asperger's Syndrome and Pervasive Developmental Disorder are part of the Autism Spectrum of Disorders. Your best bet at this point is to talk to your pediatrician about your concerns as soon as possible. If your son is enrolled with Head Start, they also offer services, including disability support, that can help guide your family towards answers. Good luck.
 
A Note: Autism and ADHD, while not mutually exclusive, are very different, and it is your right and your obligation to obtain a second opinion  on all diagnoses.

Aspergers Syndrome is a subcategory of PDD-- Pervasive Developmental Disorders. Asperger Syndrome is also considered part of the ASD's or Autistic Spectrum Disorders. It would fall into the mild autism or high functioning autism category. Asperger Syndrome is sort of a gray area that cannot be definitively diagnosed as Autism yet exhibits enough autistic traits that it can be considered a close relative (so to speak).
 
To confirm the diagnosis, continue to consult with your pediatrician and get a referral to either a neurologist or child psychologist to figure out exactly what is going on with your son. Once you have a definitive answer, you can then check for resources in your local area. Here in Los Angeles we have an organization called the Regional Center which provides services for ASD's and other conditions. Each state has different resources tied in with the local schools. Your doctors should be able to point you in the right direction; if not, the local school district should have some referrals for you.
 
Monique Zarcone
M.A. of Ed in Teaching and Learning
Mother of six; one son with Asperger Syndrome