window.onload = myRollover;

function myRollover() {
	for (var i=0; i<document.images.length; i++) {
		if (document.images[i].parentNode.tagName == "A") {
			setupRollover(document.images[i]);
		}
	}
}

function setupRollover(myImage) {
	myImage.outImage = new Image();
	myImage.outImage.src = myImage.src;
	myImage.onmouseout = rollOut;

	myImage.overImage = new Image();
	myImage.overImage.src = "images/site_structure/images/" + myImage.id + "_on.jpg";
	myImage.onmouseover = rollOver;	
}

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

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