a nerd is a socially inept, awkward loser not necessarily a smart person. he/she can be an idiot, a dull, insipid, square bunghole who doesn't know how to party. a geek is not a nerd, just someone who has exceptional qualities and who is bankable. a geek rules the world whearas nerds are totally faceless.
Bill Gates and Steve Jobs are computer geeks, whereas Richard Simmons is a faggish nerd.