Chatting in php

[Ch4s3t0ph3r]

Hello, i am currently working on a project. I have a website all in php and in order to view any part of the website the user must login. Now what i want to do is have a section for chatting, where they can click on the link and it will take them to a new page and they can start chatting. But i dont want them to re-login, i want to use the current name that they have logged in as, wen the entered the site. and i also dont want the chat room to be in a separate window, but for it to be integrated on my webpage, with my template. i have looked for days for at least sumthing that i could try to modify, but nothing worked. so, it would be great if sumone can point me into the right direction of getting this done.