You can change the look and feel of Yahoo! Messenger with Skins in either of the following two ways:

1. Click the "View" menu in Yahoo! Messenger and select "Change Skin."
2. Click the pull-down menu and select a Skin.
3. Click the "OK" button at the bottom of the window.

or

1. Click the "Messenger" menu in Yahoo! Messenger and select "Preferences."
2. Click the "Appearance" category.
3. Click the "Change Skin" button.
4. Click the pull-down menu and select a Skin.
5. Click the "OK" button at the bottom of the window.

You can add new Skins by following the instructions located here.