var suffix1 = '_off.';
var suffix2 = '_on.';

function rollOver() {
	var images = $$('img').concat($$('input')); 

	var tmp = new Object();
	images.each( function(obj, index) {
		obj.galleryImg = false;
		if(obj.getAttribute('src') && obj.getAttribute('src').indexOf(suffix1)!=-1)
		{
			obj.onmouseover = function() {
				this.setAttribute('src', this.getAttribute('src').replace(suffix1, suffix2));
			}
			obj.onmouseout = function() {
				this.setAttribute('src', this.getAttribute('src').replace(suffix2, suffix1));
			}
			tmp[index] = new Image();
			tmp[index].src = obj.src.replace(suffix1, suffix2);
		}
	} );
}

Event.observe(window, "load", rollOver, false);