How to implement Chatting feature (just like gmail and fb) for a sharepoint site?

we are trying to implement chatting feature for the share point 2010 site collection with windows authentication mode..

I search in the goggle but i didn’t find any solution. we are stuck in the following points

1) how to find the  current login users and

2) how to know whether the users are  are logged in or not after some time?

3) how to open the chat window popup,close etc….

we are trying to use custom timer jobs to find the current login users and storing in the lists and custom web part for displaying the online users .. Is it better or not?

Any help or  suggestion for best approach will help us allot.

Thanks in Advance………..