var offset = 800; 
    var padding = 500;
    var targetID = "navDiscos";
    var currentPos = 0;
    var limit = 0;
	
	$(document).ready(function () {
		limit = $(document).height() - $("#" + targetID).height() - padding;
		$("#" + targetID).css('top', offset + "px");

		$(window).scroll(function(e) {
			var topOffset = $(window).scrollTop();
			if(topOffset >= offset && topOffset <= limit) {
				currentPos = $(window).scrollTop();
				$("#" + targetID).animate({top: currentPos}, 5);
			}
		});
  });