Versuch's mal so:
function changeImage(layer,name,obj) {
if (document.layers)
eval('document.'+layer+'.document.images["'+imgName+'"].src = '+imgObj+'.src')
else document.images[imgName].src = eval(imgObj+".src")}
Wobei:
layer = <div id="layer" ...
name = <img name="name" src=" ...
obj = obj = new Image();
obj.src = "...
Guten Tag übrigens, soviel Zeit muß sein.