Login system

Dear list, I'm sorry to bother (or sorry for being stupid!) , but I've been looking around for some days and can't find what I'd like to have. My knowledge about sessions is literally non-existent and therefore I decided not to start creating a 'bycycle' from scratch. I'm looking forward for an authorisation system which stores user data (login name, password, etc.) in the MySQL and only if the user has logged on he/she has got certain priviliges across the whole site. The people who haven't logged on, can surf around, but certain features are turned off. And even more - it would be good if I could customize different users for different rights. I managed myself to do the authorisation for a single page, but don't think it is very secure. I don't want to use cookies and therefore I should be passing the SID to all URL-s, correct? Does this mean I can't really use post method with forms? Any hints, good tutorials, previous discussions? A usable script would be good... :) TIA Kristjan P.S. kanarik@zzz.ee to CC: , I'm on the digest.