Session id's

Hey PHP'ers, Hmm, I'm a bit of a session newbie, and trying to get as far away from client side dependancies as possible I decided to remove all my cookie code from a Cart system I am writing and use sessions, my problem is that I am using sessions with thier default value so as a user hits the products page a new session is started session_start() then when a user adds a item to thier cart im am trying to insert the session id l by getting its value $CartUser = session_id(); and inserting it into the database the problem is $CartUser is empty, I also tried the constant $_SID_ as well same thing, now sessions are being saved to /tmp as per manual, so why can't I get the current session's id??? Any help would be a godsend, Regards, Joseph Blythe Session Newbie