Using the IE Web Developer Tools, moving the "Page Section: Home" HTML comment to before <DIV id=main-content> in the markup made the gap disappear.
You're using rather extravagant comment formatting. Some browsers, especially early IE versions, are sensitive to comment placement, and it's not impossible that stretching them over multiple lines may cause problems too. I recommend stripping them down to single lines and with single spaces. i.e. <!-- Page Section: Home -->
Regarding the images, why are they in divs with the class "col_one_third" when the images occupy half the width of the container? This may not make a practical difference as the images simply spill out of the div whatever the browser, but it seems an inaccurate use of the class. A fix is to remove the "col_last" class from divs containing the images.