Simple. As stated above n00b is derived from, and short hand for, newbie.
n00b looks cooler than n3\/\/b. It's also quicker to type. When bashing another player in a game it's important to do so as quickly as possible. Adding unnecessary keystrokes in a taunt is likely to waste your time and distract the taunter. This could lead to unfortunate and potentially embarrassing events. The last thing a taunter wants to do is leave themselves vulnerable to a riposte at perceived imperfections.
Noob was derived by an ignorant target of such a taunt who was most obviously not 1337 enough to realize those were zeros and not the letter “O”. Not an unexpected mistake from someone deserving of such a taunt in the first place.
There you are. The history of the term noob. If you believe that. OMG ROFLPMP U R A LLAMA.
That or it could have been a typo... >_<
Edited, Wed Jan 14 12:35:20 2004 by DiplomaticWeapon