Unfortunately, you can't add any skin to the new versions of iTunes. If you're using iTunes 7.0 or below, you can add a skin with the Multi-Plugin program for iTunes. Once you found a link to download the utility, close iTunes and install the application following the on-screen steps. After that, use Google search engine to find iTunes skins and download them in the Skins folder from iTunes directory. Next, you need to launch iTunes and to open Preferences from the Edit menu. Click the Multi-Plugin option and select the skin you want to use.