They are on the docs cd, or the knowledge base.
Type skins and there are a couple of zip files.
Be aware though that these skins are bigger more detailed skins and i have had some people put new skins on and had issues.
The skins that have buts that light up when you hover over something are a nice idea but dont work that well, the colours are a bit naff aswell me thinks.
I prefer the default 4.0 one.