function getPixelsFromPage(obj){
	objFromTop = obj.offsetTop;
	while(obj.offsetParent!=null) {
		objParent = obj.offsetParent;
		objFromTop += objParent.offsetTop;
		obj = objParent;
	}
	return objFromTop;
}

    function getpage(){
    		var offs = 1500;
        var checkoffset = getPixelsFromPage(document.getElementById("page_bottom")) - getPixelsFromPage(document.getElementById("page_top"));
        if (checkoffset < offs){
        		if (document.all)
        			document.all['DisplayTop'].style.display='none';
        		else
            	document.getElementById("DisplayTop").style.display='none';
        } else {
        		if (document.all)
        			document.all['DisplayTop'].style.display='block';
        		else
            	document.getElementById("DisplayTop").style.display='block';
        }
    }
    setTimeout('getpage()',1000);