Entering Yahoo! Chat from Yahoo! Messenger is a piece of cake. Here's how:

1. Sign in to Yahoo! Messenger
2. Select Messenger from the menu bar.
3. Select Yahoo! Chat from the drop down menu.
4. Click Join a Room.
5. At the top of the window that opens, after "Enter Chat room as," select an Alias you'd like to use in this chat.
6. Select a Category on the left, and a Room on the right.
7. Double-click the name of the room you want to enter. The Chat window opens up, where you can see a list of all the people that are currently in the room.
8. Click Join Chat.

Congratulations! You're chatting!