User adjustable [VH]Boxes

[Dirk Koopman <djk tobit co uk>]

How do I get the nice adjustable Vertical or Horizontal separators like
one sees in things like evolution.

I have an app that has many windows arranged thus:-

window                   
-------------------------------------------------------------
window
------------------------------+------------------------------
window                        | window
                              |
                              |
------------------------------+------------------------------
window                        | window
                              |
                              |
------------------------------+------------------------------

I need the user to move all the separators around so they can resize the
windows how they want. 

As a separate, but related, question: How do I get the positions and
other necessary information out of which ever widgets I need, so that I
can restore those positions on startup?