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

aboutus_normal_image = new Image();
aboutus_normal_image.src = "/images/aboutus.jpg";
aboutus_mouseover_image = new Image();
aboutus_mouseover_image.src = "/images/aboutus_on.jpg";

contactus_normal_image = new Image();
contactus_normal_image.src = "/images/contactus.jpg";
contactus_mouseover_image = new Image();
contactus_mouseover_image.src = "/images/contactus_on.jpg";

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

newsletters_normal_image = new Image();
newsletters_normal_image.src = "/images/newsletters.jpg";
newsletters_mouseover_image = new Image();
newsletters_mouseover_image.src = "/images/newsletters_on.jpg";

insben_normal_image = new Image();
insben_normal_image.src = "/images/service.jpg";
insben_mouseover_image = new Image();
insben_mouseover_image.src = "/images/service_on.jpg";

claims_normal_image = new Image();
claims_normal_image.src = "/images/reportclaim.jpg";
claims_mouseover_image = new Image();
claims_mouseover_image.src = "/images/reportclaim_on.jpg";

priquote_normal_image = new Image();
priquote_normal_image.src = "/images/getaquote.jpg";
priquote_mouseover_image = new Image();
priquote_mouseover_image.src = "/images/getaquote_off.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");
}
}
}