Download the newest version of LimeWire, choose the 'View' menu option, then 'Apply Themes' and then 'Get More Themes'. On the website it brings up, download the skin you'd like via the magnet link (the one that says "Download with Magnet URN and Gnutella") -- it should automatically download within LimeWire. When it's finished downloading, it'll ask if you'd like to apply the new skin.

Doing it through the above method saves all the hassle of having to ensure that you've saved the skins to the correct directories.