Image Swapping and Pull Down Menus

Hi guys! I have a super hard question (at least for me). Okay look at this website:

http://www33.brinkster.com/instance1/TestPage1.htm

I swap images with each link you see on the top, but I need the images to swap from a drop-down menu instead of all those tabs (I can't fit all the links I need on that top space). A note: The briefcase and white box is an image I've used as the cell background, so it doesn't reload each time with the swapped image. Any suggestions?

Thanks!