[news.eclipse.platform.pde] External Jars and PDE?

["klm" <asd@xxxxxxx>]

I have made a PDE project (Hello world, control). The plugin should launch 
an application that I have written. But this application depends on another 
external jar.

I have tried to add this external jar to the build path but that does not 
work. How do I add external jars to a PDE project?