Session expire after certain inactive period

Hello, I changed the session.cookie_lifetime to 10800 (3 hr) in my php.ini as default value. Now if I close the browser after session_register or session_start has been executed, next time when I open the browser (not reached 3 hr yet), the cookie still stays. My questions are 1. should I use setcookie()? 2. what's the difference between setcookie() and just simple session_register()? 3. how can I set expire time, so if user is not active for 10 minutes, he/she is automatically logged out? 4. Upon closing the browser, user is logged out automatically (coz right now, it isn't). Did I blah too much?? =p Thank you. - Bernie