window.onload = rolloverInit;

function rolloverInit(){
	for(var i=0; i<document.images.length; i++){
		if(document.images[i].parentNode.tagName == "A"){        // parent node - link is a parent for the image and this says if parent of the image has tag A (link)
			setupRollover(document.images[i]);
		}
	}
}

function setupRollover(thisImage){
	thisImage.outImage = new Image();
	thisImage.outImage.src = thisImage.src;
	thisImage.onmouseout = rollOut;
	
	thisImage.overImage = new Image();
	thisImage.overImage.src = "images/" + thisImage.id + "_on.gif";
	thisImage.onmouseover = rollOver;
}

function rollOut(){
	this.src = this.outImage.src;	
}
function rollOver(){
	this.src = this.overImage.src;
}