floating at elastic height

I'm sure this is just a layout error, but I hope there is a way around. Simply put, if I have a variable height container div, and then a div floated to the right, and I want that floated div to always be the max height of the container div. I made some killer drawings. My issue

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What I want to achieve:

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Do you maybe have a link so I can play with it in FireBug?

If you can't post links, just add spaces to it at some places and the board won't see it as a link ...