$(window).load(function() {
    $('#slider_nivo').nivoSlider({
		directionNavHide: false,
		keyboardNav: false,
		captionOpacity: 0.7,
		afterLoad: function() {
			var margin = $('#slider_nivo .nivo-controlNav').width() / 2;
			$('#slider_nivo .nivo-controlNav').css({'margin-left' : '-' + margin + 'px'});
		}
	});
});