1. In other skins. There's also a 'Parts Library' somewhere at deviantArt.
2. To change the start button, rename the start button in the skin you've decided to change (startbutton.tga or whatever it's currently called to startbutton.bak) and then just "Copy to" the new one into the .wba file.
That should do it, and remember: You can't distribute that altered skin. It's for personal use only.