按钮控制div上下移动

http://hi.baidu.com/ada_lc/item/961b53cbd8ce723199b49864

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
<style type="text/css">
ul,li{margin:0;padding:0}
#scrollDiv{width:300px;height:100px;min-height:25px;line-height:25px;border:#ccc 1px solid;overflow:hidden}
#scrollDiv li{height:25px;padding-left:10px;}
</style>
<script src="jquery-1.2.6.js" type="text/javascript"></script>
<script type="text/javascript">
(function($){
$.fn.extend({
        Scroll:function(opt,callback){  
                //参数初始化
                if(!opt) var opt={};
                var _btnUp = $("#"+ opt.up);//Shawphy:向上按钮
                var _btnDown = $("#"+ opt.down);//Shawphy:向下按钮
                var timerID;
                var _this=this.eq(0).find("ul:first");
                var     lineH=_this.find("li:first").height(), //获取行高
                       // line=opt.line?parseInt(opt.line,10):parseInt(this.height()/lineH,10), //每次滚动的行数，默认为一屏，即父容器高度 
        line=1;//一行一行的滚动
       speed=opt.speed?parseInt(opt.speed,10):500; //卷动速度，数值越大，速度越慢（毫秒）
                        timer=opt.timer //?parseInt(opt.timer,10):3000; //滚动的时间间隔（毫秒）      
                if(line==0) line=1;
                var upHeight=0-line*lineH;
                //滚动函数
                var scrollUp=function(){
                        _btnUp.unbind("click",scrollUp); //Shawphy:取消向上按钮的函数绑定
                        _this.animate({
                                marginTop:upHeight
                        },speed,function(){
                                for(i=1;i<=line;i++){
                                        _this.find("li:first").appendTo(_this);
                                }
                                _this.css({marginTop:0});
                                _btnUp.bind("click",scrollUp); //Shawphy:绑定向上按钮的点击事件
                        });
                }
                //Shawphy:向下翻页函数
                var scrollDown=function(){
                        _btnDown.unbind("click",scrollDown);
                        for(i=1;i<=line;i++){
                                _this.find("li:last").show().prependTo(_this);
                        }
                        _this.css({marginTop:upHeight});
                        _this.animate({
                                marginTop:0
                        },speed,function(){
                                _btnDown.bind("click",scrollDown);
                        });
                }
               //Shawphy:自动播放
                var autoPlay = function(){    
                      // if(timer)timerID = window.setInterval(scrollUp,timer);//(自动滚动)
                };
                var autoStop = function(){
                        if(timer)window.clearInterval(timerID);
                };
                 //鼠标事件绑定
                _this.hover(autoStop,autoPlay).mouseout();
                _btnUp.css("cursor","pointer").click( scrollUp ).hover(autoStop,autoPlay);//Shawphy:向上向下鼠标事件绑定
                _btnDown.css("cursor","pointer").click( scrollDown ).hover(autoStop,autoPlay);
        }      
})
})(jQuery);
$(document).ready(function(){
        $("#scrollDiv").Scroll({line:4,speed:500,timer:1000,up:"btn1",down:"btn2"});
});
</script>
</head>
<body>
<div id="scrollDiv">
<ul>
    <li>这是公告标题的第一行</li>
    <li>这是公告标题的第二行</li>
    <li>这是公告标题的第三行</li>
    <li>这是公告标题的第四行</li>
    <li>这是公告标题的第五行</li>
    <li>这是公告标题的第六行</li>
    <li>这是公告标题的第七行</li>
    <li>这是公告标题的第八行</li>
</ul>
</div>
<span id="btn1"><img src="up.jpg" width="20" height="19" /></span>&nbsp;&nbsp;<span id="btn2"><img src="down.jpg" width="20" height="19" /></span>
</body>
</html>