Sorry guys but you are all barking up the wrong tree here and that approach won't work
That won't work at all I'm afraid as you cannot set any fluid elements to 100% height because that means that first they must have a parent with a known height (not content height) and if indeed they do have a parent of known height then you have effectively trapped your content in a 100% high container that can never expand. Just add content to go below the fold in any of your columns to see why this won't work.
The CSS faq explains 100% height in detail and why you can never use it like this.
You may think that you could use min-height:100% instead but that won't work either for multiple nested elements. You can effectively only ever have one min-height:100% nested element as a child cannot base its height on a parent that is defined by min-height - the height collapse to auto. You could have separate (non nested) elements basing their height off html,body set to 100% but that won't mean that the columns will equalise. It just means that initially they will extend to the bottom of the view port but when one grows the others won't follow and you are back to square one :). It's a catch 22 situation.
Read my article on equal columns for a better understanding.
The easiest solution is to create a background gif in the side columns color and just repeat it on the parent that is holding both columns (the image would be as wide as the side column and about 10px high. You should also include the side border on the column). Give that parent a background color also and you will get your two equal columns very easily (called faux columns).
The other alternatives are negative margin techniques that complicate the mark up a little or my absolute column overlay technique which means adding extra mark up.