I’ve managed to customize my dock’s skin using Leopard Docks. You will need to do some file replacing in the system folder. This is how you do it:
Go to Macintosh HD > /System/Library/Core Services/
Right-Click on “Dock” and select “Show Package Contents”
Go to /Contents/Resources/
Backup the files you are about to replace (Incase you did not listen, here they are)
Move those same original files to the trash
Move the files you downloaded to that folder
Open Terminal and type “killall Dock” (without the quotes)
View your nice new dock.
This is a tip courtesy of Juan of The After Mac.