Geek just indicates strong interest. Road geeks, for example, spend unusally high amounts of time studying the interstate system and beyawtching about how the government needs to hire them to run the SHA's and stuff because they're not handling the situation appropriately. And they're damn proud of it. The same applies for computer geeks - and car geeks.
Nerd indicates the whole look and feel thing - white dress shirt, black slacks, pocket protector, taped glasses, along with high grades across the board.
Dork is a whale penis. Dork is DEFINITELY the worst (And no, it probably doesn't refer to your virility - whale penii are very long, but very floppy)