newbie- a begginer or inexperienced player
noob- generally means someone who is obnoxious, annoying, or breaks the rules or cannot play effectively; whether they are actual newcomers or not is mostly irrelevant.
thats what noob and newbie actually mean.
http://en.wikipedia.org/wiki/Noob
personally i think a newb is any one who is inexperienced in something, like i am a newb in programming
but a noob is some one who is annoying and uncunstructive, like the ksers on conquer or the newbs who wont shut up about wanting to get plvled
so on the forums, u can be a noob and have a relativly high post count and karma, but u can also not be a noob and have 10 posts and no karma.