Using a skin
In order to use skins you have to switch to the skins2 interface. To do that do the following: Start VLC, open menu "Preferences", select "Interfaces" and click "Main interface". Change the setting in the drop-down menu "Interface module" from 'Default' to Skinnable Interface. Click the 'Save' button and restart VLC. To change get the old interface choose 'Default from the "Interface module" drop-down menu.
Adding a new skin
To add a new skin go to the Skin page, choose a skin and click the "Download" link. Alternatively you can obtain the 'Skin Pack' which contains all available skins.
In addition to the skins listed on the 'Skins Page', VLC supports all Winamp2 and XMMS skins (.wsz files).
To install, move the skins' ".vlt" file to the 'VLC\skins' (Linux users ~/.vlc/skins2/) directory. For the the 'Skin Pack' goes: unzip it to 'VLC\skins'. Each skin will have it's own sub-folder created containing it's files.
Finally, to set the skin, right-click in the title bar or control bar, go to 'Select skin' and select the desired skin.