Can you attach a real size screenshot of the layout you posted in your first post as it will give me something to better work with and see what can be done?
Is the sidebar on top of the stripy background and what content is to go into the sidebar?
If I understand correctly then I feel you may need to look into using a min-height:100% wrapper as in the example I posted previously which gives you all the height you need to apply images without needing a fixed height. The middle section looks awkward though and would probably need to be done with a min-height in pixels to get an initial height if the content is short.
If you can post a full size screenshot then I will see if I can cut it up and insert it into a structure or at least give some better pointers.