home_off = new Image();
home_off.src = "/images/home_off.jpg";

home_on = new Image();
home_on.src = "/images/home_on.jpg";

about_off = new Image();
about_off.src = "/images/about_off.jpg";

about_on = new Image();
about_on.src = "/images/about_on.jpg";

services_off = new Image();
services_off.src = "/images/services_off.jpg";

services_on = new Image();
services_on.src = "/images/services_on.jpg";

people_off = new Image();
people_off.src = "/images/people_off.jpg";

people_on = new Image();
people_on.src = "/images/people_on.jpg";

publications_off = new Image();
publications_off.src = "/images/publications_off.jpg";

publications_on = new Image();
publications_on.src = "/images/publications_on.jpg";

careers_off = new Image();
careers_off.src = "/images/careers_off.jpg";

careers_on = new Image();
careers_on.src = "/images/careers_on.jpg";

offices_off = new Image();
offices_off.src = "/images/offices_off.jpg";

offices_on = new Image();
offices_on.src = "/images/offices_on.jpg";

press_off = new Image();
press_off.src = "/images/press_off.jpg";

press_on = new Image();
press_on.src = "/images/press_on.jpg";


<!-- repeat the 4 lines above for any subsequent images. -->

function swap(){
if (document.images){
for (var x=0;
x<swap.arguments.length;
x+=2) {
document[swap.arguments[x]].src = eval(swap.arguments[x+1] + ".src");
}
}
}