Configuring yahoo messenger on iChat
You will need to sign up for a Yahoo! account by going here. 

Once you have done that, you can configure Yahoo Messenger in iChat by doing the following:


Open iChat
Open iChat Preferences by going to the menu item iChat > Preferences or by hitting &#8984; + , on your keyboard
Go to Accounts
Click the + button
Select "Yahoo" from the drop down menu under Account Type:





Authenticate using your Yahoo account credentials
Enjoy using iChat with Yahoo.