The solution is called bitlbee and CGI-IRC.

Bitlbee

This little application runs as a service on your Linux box and acts as a gateway between all common messenger networks (Yahoo, MSN, Jabber, ICQ) and a normal IRC frontend. This makes it possible to use an IRC application to access all these networks.

CGI-IRC

This is a nifty little CGI script that works like an IRC application and can connect to any IRC network. In our case it should connect to the bitlbee server I just mentioned. It works well on Firefox 1.x or Internet Explorer 5 to 6.

Take a look at this screenshot, it reflects my working implementation of the above described system:

Not only that, but on a machine that does not allow the user to install any application, making it accessible from internet cafes or your friends computer in china.