Software measuring online chat group participation

I am in the early stages of setting up a Web site with a chat server that allows for real-time text-based communication between groups of folks with similar diagnoses. I would appreciate information on software that would keep track of who attended the online meetings, for how long, how often, etc. If any of you could steer me in the appropriate direction I would sure appreciate it. Thanks in advance

• Resource for Software by Gil Levin, 9/18/96
• Software measuring online chat group participation by Clarke S Harris PhD, 12/1/97