Here are some useful links

Official Support page:
http://na.blackberry.com/eng/developers/themes/

Tools and Downloads - http://na.blackberry.com/eng/develop...s/devtools.jsp
Simulators (used while testing themes) - http://na.blackberry.com/eng/develop...simulators.jsp
FAQ - http://na.blackberry.com/eng/developers/themes/faq.jsp

Creating theme using Plazmic Theme Builder (Video) -http://www.blackberry.com/DevMediaLibrary/view.do?name=CDK4_6Demo