Sarah,
I think you're looking to the correct enablement to trigger your action. Here is the appropriate contribution from Spring IDE's plugin.xml
Code:
<extension
point="org.eclipse.ui.navigator.navigatorContent">
<actionProvider
id="<your id>"
class="<your action provider class">
<enablement>
<or>
<and>
<instanceof value="org.eclipse.core.resources.IFile"/>
<test property="org.springframework.ide.eclipse.beans.core.model.isBeansConfig"/>
</and>
<instanceof value="org.springframework.ide.eclipse.core.io.ZipEntryStorage"/>
<instanceof value="org.springframework.ide.eclipse.beans.core.model.IBeansModelElement"/>
<instanceof value="org.springframework.ide.eclipse.beans.ui.model.metadata.BeanMetadataNode"/>
<instanceof value="org.springframework.ide.eclipse.beans.core.model.metadata.IBeanMetadata"/>
</or>
</enablement>
</actionProvider>
</navigatorContent>
</extension>
Have a look at BeansNavigatorActionProvider class to see an example on how we add the actions to the menu.
HTH.
Christian