"Dork" is something like "geek" and "nerd," but "dork" doesn't have the brainy connotation of the other two. "Dorks" are considered socially awkward, uncool and often physically inept--but not necessarily supersmart.
Legend has it that "dork" appeared in the slang of American teens in the early 1960s. Originally it meant penis--a combination of the word "dick" and "dirk" (slang for a small knife). A decade later, "dork" had come to mean a clumsy, foolish person and it's used in this sense most often today.
"Dork" is a playful word--and so is "dorky." Clothes, names, parents, younger siblings or even friends can be dorky. Single-minded but harmless devotion can make you a dork; "band dorks," for example, spend all their time practicing and hanging out with other musicians.
There's plenty of dork pride to be found on the web these days. Just take a look at a site like Dork.com. There is a dorky comic book publisher (Dork Storm Press) and even a tongue-in-cheek quiz to determine your dorkiness.