No. To use Yahoo, you'll have to get either Yahoo's official messenger, or a third-party client like Adium (http://adiumx.com) or PSI (http://psi-im.org). If you have a jabber account with a Yahoo transport you can setup PSI or other jabber client to register with that account and then add your jabber account to iChat. See http://timmargh.net/archive/2005/05/use_msn_yahoo_o.php for details.
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