To influence the layout of you screens in jZeno, you can create an implementation of the net.sf.jzeno.echo.Layout interface. The javadoc of this interface describes in details what each method has to do. A good starting point would be deriving a class from the AbstractLayout class, which partly implements the interface for you.
A good place to look is the source code to the net.sf.jzeno.echo.ZenoLayout, which is the default layout used by the jZeno demos, etc...