Hi are you after free information or paid for information?
If you open up the skinning documentation, open up the default skins you can get a very good start on it.
I have a few things on my site to help people get started, but the first thing you can do is read through the skinning documentation and get a grasp on it.
dnncreative.com does have some tutorials you can pay for, I have a tutorial you can pay for, but there should be enough information if you know html and slicing photoshop files to get you started.
Nina Meiers