I had a request for articles on explaining an Asperger's diagnosis to siblings, and here are a couple of articles I found from kidshealth.org. I like the article for teens better, as it is a little more positive and it addresses Asperger's directly. The article for kids is a little more basic, and just addresses autism in general.
For kids: http://kidshealth.org/kid/health_problems/brain/autism.html
For teens: http://teenshealth.org/teen/diseases_conditions/learning/autism.html
My Friend with Autism: A Coloring Book for Peers and Siblings