who's logged on / how to I find out about other sessions

Hi, I'm writing a bbs/messageboard system and am trying to figure out how to tell what other users are logged on. I know I could store the info in a table in my login code but then how do I find out if people are logged out with out making them actually use a logout button or the like. I was going to do it that way but I have noticed that phpnuke sites can list the number of logged in sites etc; but their code is a little beyond me atm Is there a way to list other session vars ? any ideas welcome with thanks Christian Christian Cable ICT Assistant Careers Service; Lancaster University Tel: (01524) 594072 Fax: (01524) 592072 http://www.lancs.ac.uk/staff/cable/