Howto correctly generate "expandable void"?

["Till Harbaum / Lists" <lists harbaum org>]

Hi,

i have a vbox with a bunch of buttons. I want some of them to appear at the top
and some of them at the bottom. The buttons should not be expanded and the
space between them should also not expand except the space between the two
groups. Something like this:

(a)
(b)
(c)




(x)
(y)
(z)

How is this done correctly without having some invisible item i can place between
both groups and which is set to expand/fill?

Till