Could anyone suggest a good tutorial or provide some info on how the user logged in system works in the chat section at google mail? I have a similar system with php that displays all usernames of people that have been made activity in the last five minutes but i really wanted the funcionality of the google system. Im sure its not overly hard but im not adepth at ajax and cant figure a way to get it working.

BAsically if you havent seen how googlemail works a user clicks sign in to chat and their name appears to all other users without the page reloading.

Could anyone help. Ive scoured google for hours. I can post my php system if tht helps