attachRollOverEvent = function(imageId){
$(imageId).mouseover( function(){ $(this).attr("src", $(this).attr("src").split('_off').join('_on')) } );
$(imageId).mouseout( function(){ $(this).attr("src", $(this).attr("src").split('_on').join('_off')) } );
}
$().ready(function(){
attachRollOverEvent(".rollover");
});