[Darvin]

Newb and Noob both come from the root "Newbie", which simply means someone who is new to the game. Everyone's a newbie originally, it's not really a bad thing. Generally "newb" is regarded as shorthand for newbie and the meaning is the same. "Noob" however has taken on the negative connotations of the word, meaning someone who plays as if they have no experience in the game. Often "noob" is used as a derogatory term for no other reason than to put down the player. As such, I avoid that particular spelling.

There are also other spellings, like "nub", but generally they fall under the category of the "noob" spelling of the word.