Restricted site area access

Hi all, Please forgive the newbie question, any help/guidance would be much appreciated! I am planning to implement quite a large site using PHP and MySQL. This site is to contain areas which are public and areas which require logging in. There is to be 3 or 4 different levels of users, with each level being privilege to a different selection of pages. My question really is a fundamental PHP/MySQL one. My first thought was to store all the usernames and passwords in a (MySQL) table with a field for userlevel. Point of concern with this was how safe would it be? Also, assuming these users all logged in from the same point in the site, how would one/how easy is it to keep track of which one of the 5 levels (public, UL 1-4) the user is at and make the page display accordingly (or not as the case may be). My first two immediate ideas was some use of cookies, or passing some variable between pages (session ID) Sorry if this question is overly basic, but it's something I've been pondering over for quite some time now! Cheers, Tom Tom Carter Web Programmer roundcorners.com