// JavaScript Document
normal_image = new Image();
normal_image.src = "graphics/facebook_bt_1.jpg";

mouseover_image = new Image();
mouseover_image.src = "graphics/facebook_bt_0.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");
}
}
}