Rollover mediante Jquery

 $("img#modificabt").hover(
 function(){
 toNormal = $(this).attr("src");
 toOn = "public/img/buttons/modificar_on.gif";
 $(this).attr({
 src: toOn
 });
 },
 function(){
 $(this).attr({
 src: toNormal
 });
 }
 );