A nerd is a person with strong understanding of technical fields with little to no understanding/interest in social grace.
Example: A computer nerd lives in his basement and writes programs all day. He knows Unix, Linux, and posts on messageboards. If he is seen at Technical events, it is awkardly and not a good experience interacting with others.
A geek is a person wtih a strong disposition to technical fields but may or may not have understanding of social graces.
This person could love gadgets, might be into programming, graphics, heck, even comics, art, movies, or theater. They have an above average insight into technical related fields and will gush about them when asked. They can blend into crowds with little trouble, and while they might not personally prefer a social setting, they know how to act when in one.
A dork is a person with some disposition to technical fields but with little to no understanding of social grace.
Example: A gamer who doesn't come out of his room/basement. Above average interest in technical subjects, but lacks the further knowledge to make him a nerd.
I am a Nerd in regards to computers, programming, hardware, and Gaming. I am a geek when it comes to Comics, Scifi, Books, and Costuming.