function unitRollover() {
	if(!document.getElementsByTagName) return false;
	
	loadImages = [];
	
	var image = document.getElementsByTagName("img");
	var imageCnt = image.length;
	
	for(var i=0; i < imageCnt; i++) {
		var images = image[i];
		var imagesSrc = images.getAttribute("src");
		
		if(imagesSrc.indexOf("_off.") != -1) {
			images.oriSrc = imagesSrc;
			images.onSrc = imagesSrc.replace("_off.", "_on.");
			
			loadImages[i] = new Image();
			loadImages[i].setAttribute("src", images.onSrc);
			
			images.onmouseover = function() {
				this.setAttribute("src", this.onSrc);
			}
			images.onmouseout = function() {
				this.setAttribute("src", this.oriSrc);
			}
		}
	}
}

addLoadEvent(unitRollover);