image1 = new Image();
image1.src = "images/anim/1.jpg";

image2 = new Image();
image2.src = "images/anim/2.jpg";

image3 = new Image();
image3.src = "images/anim/3.jpg";

image4 = new Image();
image4.src = "images/anim/4.jpg";

image5 = new Image();
image5.src = "images/anim/5.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");
}
}
}