Dock Library is a free application that takes the headache out of managing styles for your Leopard dock.
Download styles from sites such as LeopardDocks.com or LeopardDocks.net. Once downloaded, there's no need to expand or unpack the file, just click "Import" to add it to Dock Library.
When you have some styles in your library, you're a simple click away from changing the look of your dock. No hunting through hidden system directories, just select the dock you want and click "Activate".