normal_image1 = new Image();
normal_image1.src = "../images/joinus_off.gif";
mouseover_image1 = new Image();
mouseover_image1.src = "../images/joinus_on.gif";

normal_image2 = new Image();
normal_image2.src = "../images/loans_off.gif";
mouseover_image2 = new Image();
mouseover_image2.src = "../images/loans_on.gif";

normal_image3 = new Image();
normal_image3.src = "../images/insurance_off.gif";
mouseover_image3 = new Image();
mouseover_image3.src = "../images/insurance_on.gif";

normal_image4 = new Image();
normal_image4.src = "../images/products_off.gif";
mouseover_image4 = new Image();
mouseover_image4.src = "../images/products_on.gif";

normal_image5 = new Image();
normal_image5.src = "../images/account_off.gif";
mouseover_image5 = new Image();
mouseover_image5.src = "../images/account_on.gif";

normal_image6 = new Image();
normal_image6.src = "../images/interest_off.gif";
mouseover_image6 = new Image();
mouseover_image6.src = "../images/interest_on.gif";

normal_image7 = new Image();
normal_image7.src = "../images/savings_off.gif";
mouseover_image7 = new Image();
mouseover_image7.src = "../images/savings_on.gif";

normal_image8 = new Image();
normal_image8.src = "../images/investment_off.gif";
mouseover_image8 = new Image();
mouseover_image8.src = "../images/investment_on.gif";

normal_image9 = new Image();
normal_image9.src = "../images/cal_off.gif";
mouseover_image9 = new Image();
mouseover_image9.src = "../images/cal_on.gif";

normal_image10 = new Image();
normal_image10.src = "../images/forms_off.gif";
mouseover_image10 = new Image();
mouseover_image10.src = "../images/forms_on.gif";

<!-- 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");
}
}
}