Integrating messenger to an existing website

Question

For an existing website and the users in it,how to integrate a chat application like yahoo or gmail or any other with minimum code changes.

Answer 1

Ajax IM looks very good for this.

Alternatively, maybe something like PHP121?

These are both instant messenger style chat systems. If you're looking for something more like a chatroom, I have used Ajax Chat successfully in the past.

I think you'll need a fair bit of code changes however you approach this, if you want to support your existing groups of users.