This is not a usual stuff. In principle, it can, but the application such technologies are very limited, first of all, by the browsers. You could be better off using a custom chat client (not a Web browser). The techniques based on Ajax present hidden pull techniques anyway. The real thing is HTTP server push.
What you need to look at is called "server push". Please see:
http://en.wikipedia.org/wiki/Server-push[
^].
—SA