$(function() {
ro = {
    rollClass: "roll",
    overSrcAddOn: "_on",
    preLoads: [],
    init: function() {
        var imgs = document.images;
        $("img.roll").each(function(i) {
        	var oversrc, t, s;
        	oversrc = this.src.toString().replace(".png", ro.overSrcAddOn + ".png");
        	ro.preLoads[i] = new Image();
        	ro.preLoads[i].src = oversrc;
        	$(this).hover(
        		function(e){
        			t = e.target;
        			s = t.src;
        			t.src = s.replace(".png", ro.overSrcAddOn + ".png");
        		},
        		function(e) {
        			t = e.target;
        			s = t.src;
        			t.src = s.replace(ro.overSrcAddOn + ".png", ".png");
        		}
        	);
        });
    }
}
ro.init();
});