Divs really aren’t intended to work like that. What are you intending to do with the 100% height div? Sometimes you can fake things using background images… depends what you are going for. Tables can be used to get a 100% height, but using tables for layout is generally frowned upon.
the site im working on has the same sort of style as a wordpress site, like a side bar down the side, but the sidebar has a differant background image to the main background and i wanted it to all the way down to the bottom.
A div will only extend as far as it’s content needs it to – so you’ll have to fake it using a bacground image that spans the whole page, but has an area designed to look like a separate column. Try this article http://www.alistapart.com/articles/fauxcolumns/ to get the full picture (no pun intended!).