Determining user logged and limit posts

Hi,
I have some general newbie questions:

First, how does the system determine if someone is logged in or not. I used the lngLoggedInUserID variable, and from my understanding, if you are not logged in it is 2, and if you are admin it is 1. But I'm not sure how is the rest of the numbers determined.

Second, is it possible to limit the number of posts someone can post per day? 5 posts in one hour doesnt seem discouraging enough.

Thanks.