Last night I found some nice tutorials/demos on how to use Enterprise Architect on the website of Sparx Systems.

They also have some UML tutorials and how to create your own design patterns in EA. They have already created the classic patterns from GOF, you can download them on http://sparxsystems.com/resources/developers/uml_patterns.html. I didn't try this out yet so let me know how good (or bad) it is.