session management and user authentication in php based app

Hi all,
I am planning to develop a web application using php and MySQL, which is going to handle around 1000 users simultaneously in some conditions.being a fairly new to this language its getting tougher for me to get things right for session management and user authentication.
it would be a great help if anybody suggest me some idea or preferably some code for implementing the same.

any suggestion or help is most welcome.

thanks & regards
nitin ashish