PHP Graphical Chat?

How feasible is this?
Would it even be possible to create an animated graphic chat program (a bit like habbo hotel - but less kiddie) using just php, html and javascript? would the server load be just too imense to be practical.
At work we get private project time and I have an idea but for the sake of project longevity I dont want to use shockwave - (director hasnt been updated for over 2 years)
A friendly user interface is absolutely key for the idea to work - would it just be too clunky, slow and server loady to work?
I guess flash is an option but I dont know how easy it is to integrate flash and php

I'm guessing here, but to reduce server load to a minimum all animation and such would have to be preformed on the client; perhaps AJAX (or what they call it today) could be employed here.
If you say animation, "Flash" is the first thing that comes to mind; whether it can be integrated with server side or client side script with remote access I really couldn't tell.