Squareness is the hallmark of a nerd. A nerd wants to fit in, but will fall back on intellectual abilities when flustered. A nerd is often found tooling--not for the love (then it would be geeking), but rather because it's a prudent investement of time and effort into the future.

Nerds lack personality

Nerds do very well within the rules given them.

Hygiene is observed
Style is generic/lacking/staid/conformist

Obsession is the hallmark of the geek. A geek really gets into it, whatever it is. They're getting something out of it. They're learning a whole hell of a lot because they have the love for it.

Geeks got personality.

Geeks beat upon the rules. They spend time geeking on the rules. Sometimes they learn them well enough to start hacking them. (This is why I think about law school.)

Hygiene is often neglected
Style is often eccentric

dork (orthogonal quality)
A dork is someone with a glitch in their social game--they respond inappropriately (do something dorky) at inopportune times. Some people become nerds and geeks because they are hopeless dorks.

(no comment on dorks w/r/t the 'rules/hygiene/style' axes)

loser (may be orthogonal)
Someone that consistently loses. Often they are bitter and otherwise socially maladjusted.

They consistently get screwed by the rules. They tend to misunderstand them and/or reflexively react to them in a detrimental manner.

Being that they can't win, they either give up or go overboard on style/hygiene/etc.