You can add a toolbar to any layout container
and you can add a separator above it. Anyway,
to visually relate the toolbar to the menu bar
it often helps to use a design for all three
components.

I provide free L&f implementation that have
optional settings for relating menu and tool bar.
You can test drive the 4 L&f in that package
and can try the menu/tool bar options in a demo
http://www.jgoodies.com/freeware/looksdemo/

In the launcher select the "Menu- & Tool Bar" tab,
select a "Header" hint, then click "Launch Demo".
I recommend to define a logical "Header" hint
but you can override border settings tool

Even if you don't use these L&fs you can copy
the visual design or use the Looks sources as
a starting point for your custom solution.

- Karsten Lentzsch