The #topNavigation div is what contains the background image of the graphic of the girl. I think the most flexible way to handle this would be to adjust the height of the #topNavigation div in the CSS so that it doesn't show the girl anymore. Then you can add another div, called #slideshow for instance, on the same level and after #topNavigation. This will you give you a new div area where you can put your slideshow.
The other approach would be just adding a new div inside the #topNavigation div and positioning that where you need it to go. This way would preserve the graphic of the girl, but allow you to put stuff on tope of it.