Try using GAIM. It does a great job of integrating many chat clients such as msn, yahoo, mirc, icq and so on. It is a free download and you can find it if you google GAIM. Unfortunately it does not support realchat, which is too bad because firefox and my antivirus software does not like realchat.

It also has the advantage that if you have more than one hotmail account that you want to chat from or yahoo account then you can also have them running at the same time using GAIM.