My website has several hundreds of users around teh world that login to the website periodically. The user information is stored in an Access database. The website is bulit with  asp.net 3.5

 

I want to add IM that is similar to Facebook. Means: When a new user login I would like him to be added to the users "online". A click on a button will open a popup flowting window that shows all the users that are online (and different list offline). The users can send messages to each other, etc. 

 

The quetsion is:  What of the different version of the Chat/IM is good for me?