Live chat application required similar to Facebook chat

Hi, I have a task management software developed in PHP which I use only within my organisation. Approximately 30 people work in my organisation, and they always stay logged in to the application. I want to have a live chat facility into my application to allow my users chat with their colleagues. I like the chat facility which Facebook offers. I want exactly the same thing, can somebody do this? Everything should be exactly the same as Facebook chat. Like, there will be a button on the bottom where I can click to see all the logged in users, and start chatting with somebody. There should also be sound notification. In one word, exactly same like Facebook chat. Please let me know how much it will cost and within how long you can deliver it. If you have any question let me know. Thanks. Sumon