Like some other people in this thread, I like to differentiate between newb and n00b. A newb is just a new player to the game, that's getting acquainted with how to play and will generally get better over time. Newbs usually type decently and have some semblance of intelligence, despite still being mediocre players. Newbs, unlike n00bs, can actually learn from their experiences and may quickly become a better player. Probably everyone could be considered a newb the first time they're playing.
A n00b, on the other hand, is just some moron who, no matter how long he or she plays, will remain terrible at the game. They can't spell, may use 1337 with no sense of irony, and are pretty easily insulted or offended. It seems they can't understand why they're so bad at the game, so whenever someone defeats them they're the first to call 'HACKER!!!' or 'CHEATERS' or some narsense. They're pretty amusing.