Chat Server Application

I need to make/get a freeware for a chat server software. The requirement is a web-based site where people can chat with a specific person.
 
For example, admission committee's of some B-schools in US hold admission and information chat sessions. So prospective students are told a specific time and url and they can log in and chat. Another example would be the site rediff which hosts chat at specific times with eminent personalities etc. 
 
Is there a freeware for this? My application is for an intranet and not the internet.
 
Thanks!

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