var name                    = "#sidebar";
var sidebar_top_limit       = 100;
var sidebar_top_margin      = 20;
var sidebar_slide_duration  = 500;


$(window).scroll(function() {
 
	offset = $(document).scrollTop() + sidebar_top_margin;
	 
	if(offset < sidebar_top_limit)
	    offset = sidebar_top_limit;
	 
	$(name).animate({top:offset},{duration:sidebar_slide_duration,queue:false});
	
});