You can also go to the AlienWare website.
Alienware Computers - Custom-Built Gaming Desktops and Notebooks
They have their own program name 'AlienGUIse'
You can find it here: Alienware: AlienGUIse Theme Manager
The program is simple. You choose a list of their skins, wait about 3 mins while it does it. Done.
You can ALWAYS choose the default XP skin too!
Try it for yourself.