[CSS] Problem with div height

[RedPillow]

I got this picture here: http://imageshack.us/photo/my-images/17/probmb.png/

What I need to do is to make that blue bordered div stretch in height so it fills the cyan bordered area, depending how long the red bordered area is.

So if there's lots of text in the red bordered area, the cyan-area will get a lot longer and therefore the blue area must stretch so it reaches the bottom of the wide area.

Lol do you get me 

The blue bordered area should be kind of 'anchored' into the bottom of the big white area so it stretches.

[Ampa]

Do you have a live version of the page uploaded somewhere?

It will be easier to experiment and see the structure of the page from a real example rather than a static image.