Three widgets inside resizeable panes

[Miguel Guedes <miguel a guedes gmail com>]

How can I implement three widgets inside horizontally resizeable panes, 
as given:

+-------------+-------------+-------------+
|             !             !             |
|             !             !             |
|             !             !             |
|             ~             ~             |
|     w1      ~      w2     ~     w3      |
|             ~             ~             |
|             !             !             |
|             !             !             |
|             !             !             |
+-------------+-------------+-------------+


I tried creating two h-panes and then placing w1 and w2 inside the left 
h-pane, followed by w2 and w3 inside the right h-pane but that didn't 
work because w2 is in two containers simultaneously.

Could someone please let me know what I am missing here?