var preloadFlag = false;

function newImage(arg) {
if (document.images) {
rslt = new Image();
rslt.src = arg;
return rslt;
}
}

function changeImages() {
if (document.images && (preloadFlag == true)) {
for (var i=0; i<changeImages.arguments.length; i+=2) {
document[changeImages.arguments[i]].src =
changeImages.arguments[i+1];
}
}
}

function preloadImages() {
if (document.images) {

topimage1_on = newImage("images/top_image2.gif");
topimage2_on = newImage("images/top_image3.gif");
topimage3_on = newImage("images/top_image4.gif");
preloadFlag = true;
}
}