Forthesun:
My 5 year old son has many of the symptoms of Asperger's too, although I was told that except in very severe cases they don't typically diagnose at such a young age. At this point his "official" diagnoses are ADHD and SPD, and the developmental pedi said we'd reevaluate in a few years.
I started out reading some books and filling out some checklists I found online. I discussed them with my pedi, who referred me to a developmental pedi, where my son was evaluated.
Here's my lay person's explanation:
Asperger's is a form of Autism, with a few major differences from classical Autism.
People with Asperger's are always of at least normal intelligence. There's a misconception that they're all extremely intelligent, and it's true that many people have one or more areas of giftedness, but it's not a requirement for a diagnoses.
People with Asperger's typically do desire some social interaction, but find it very difficult to maintain the give and take of normal relationships. They can come off as being very self absorbed, wanting to talk only about their areas of special interest.
In my son's case, at 3-4-5 years old, it's looked like this:
Levi has always been ahead of his peers academically, seeming to just soak up knowledge. On the other hand, as soon as you put him in a room with other children, it becomes obvious that he has no idea what to do with them. He typically chooses to play by himself. The other kids don't do things "right."
He comes off as very charming and precocious to adults, because of his large vocabulary. Everyone has always said he's like a little man, not a child. He'll lecture anyone who will listen about his favorite topic. (Currently it's Pokemon. For several years it was trains.) It's very hard to divert his focus to any other topic. It's way over and above your average kid liking Batman or whatever.
He makes poor eye contact, and may stop talking in the middle of a sentence and take off running.
There are other symptoms, but those are the ones an "outsider" might notice first.
He has many other issues relating to ADHD and SPD. Oftentimes a child on the Autistic spectrum will have one or more other diagnoses along the lines of ADHD/SPD/anxiety/ocd, etc. They all seem to fit together.
There's no cure, but many different kinds of treatment, some of dubious value.
In my limited experience at this young age, the most helpful thing has been trying to very explicitly help him learn about social expectations. "When they say this, you say this." "When you say or do this, people think that's rude, and aren't going to want to be friends,"
The good news is that a child with Asperger's can grow up to live a fairly normal life, even if they're always seen as being a little geeky.

It also important (imo) to remember that these kids are unique individuals, created by God. While they're challenging to teach and raise, they bring their own unique gifts and perspectives into the world.