Getting Div to float to bottom of parent div?

Hi I have a simple sidebar inside a div which has height:100% and I need the sidebar to float as high as the container becomes. Since I have a content div, and the content div will change on each page, it's inside this parent div which ideally should change in height and thus the sidebar would run the entire height of this parent div.

http://mibsoftware.us/clients/weber/?page_id=2

However in the above link I'm u开发者_运维百科nable to get that to work. What am I doing wrong here? Any help would be greatly appreciated!

See:

Equal Height Columns with Cross-Browser CSS

Get it to float BELOW the bottom of that div (possibly in a simillar div), and then set it's position to relative and top: -height_of_div px.