With the recent integration of chat into Yahoo! Mail Beta you're now able to chat with other Yahoo! users in your mail window.
In the meantime, you can simultaneously chat in Yahoo! Mail and IM in Yahoo! Messenger if you've got two different IDs and are signed into each separately.
The Chat option in your Yahoo! Mail Beta cannot be removed. You can, however, set your status to "Offline.”
If you're automatically signed out of Yahoo! Messenger when you sign into your Yahoo! Mail account, and if you'd rather this not happen, please do the following: