Yahoo does not support 3rd party emoticons except the ones that come with the software itself or though an add-in. There is SweetIM that can help with adding emoticons to Yahoo, but that product is considered malware. In other words, you can't add MSN emoticons to Yahoo and even if you would succeed adding them, all the persons who you would want to send your imported emoticons will need to have them installed, otherwise all that they will see is just text symbols like (":),:D,:P").