VITO have released a free for personal use theme editor for the P900. The software enables you to design your own themes for the P900 in an eay to use Windows UI.

The theme editor is available here: http://vitotechnology.com/products/P900_ThemeEditor.html

Author's Info:
New way to express yourself with VITO ThemeEditor for SE P900!
VITO ThemeEditor is a FREE for non-commercial use PC-based application that allows you to create your own themes for using on the P900.

Start with basic settings, such as defining a default color scheme, then set backgrounds and behaviour for every screen element, and finish your masterpiece with creating advanced masks and image patterns. Every setting is optional, and you can skip any step.

Variety of settings for both Flip Open and Flip Closed modes, options for editing sounds and screen saver bring endless opportunities to customize your P900.

Created themes can be saved as a single file and transferred to the P900 or exchanged with your friends and other people.