Sony has released a program to help you create your own PlayStation 3 XMB themes. The program is a windows command line application and comes with detailed instructions on how to create your own themes. Also in the package are some sample icons and images to help you get started. The process for creating custom themes is fairly easy, however, it does require a lot of graphic editing work. You can download the package below, as well as download three official XMB themes.
If you are having trouble making a theme, please see our Tutorial. Additionally, the PDF file found in the download archive will also help with editing and creating your own themes. The Theme Creator is a Windows command-line application (it will only run on Windows systems using MS-DOS).