The compilers says it can't find the DiagramTemplateLauncher class though I have org.eclipse.papyrus.diagramtemplate, org.eclipse.papyrus.diagramtemplate.edit and org.ecplipse.papyrus.diagramtemplate.editor in the plugin's dependencies.
I am running Eclipse Juno with the latest papyrus.
The package containing DiagramTemplateLauncher is not exported, which means it is not visible outside of the *.editor plug-in. I should probably fix that, but we haven't planned a new build until Juno SR2 (02/2013). You'll probably have to rely on a nightly build until then.