<style type="text/css">
div.container{height:80px;width:300px;overflow:hidden;}
div ul{margin:0px;padding:0px;}
div li{height:20px;width:100%;overflow:hidden;}
</style>
<div class="container" id="dv">
<ul>
<li>11111111111</li>
<li>22222222222</li>
<li>33333333333</li>
<li>444444444444</li>
<li>55555555</li>
<li>6666666666</li>
<li>777777777777777777</li></ul></div>
<input type="button" onclick="move(-1)" value="上一个" />
<input type="button" onclick="move(1)" value="下一个" />
<script type="text/javascript">

    function move(dir) {
        var dv = document.getElementById('dv');
        dv.scrollTop += dir * 20;
    }
</script>

------解决方案--------------------
点击时移除第一个li，再添加一个li就行了吧，简单
<button type='nutton' onclick="btnclick();">点击</button>
<ul id='ul1'>
<li>1</li>
<li>2</li>
<li>3</li>
<li>4</li>
</ul>

<script>
function btnclick()
{
 var ul1=document.getElementById('ul1');
 var lis=ul1.getElementsByTagName("li");
 ul1.removeChild(lis[0]);
 var newli=document.createElement('li');
 newli.innerHTML='5';
 ul1.appendChild(newli);
}
</script>

------解决方案--------------------

HTML code
<style type="text/css">
html,body,div,ul,li{margin:0;padding:0;border:0;vertical-align:baseline;}
#myTest{width:100px;height:80px;float:left; overflow:hidden; border:1px solid #bfbfbf;}
#myTest ul{ list-style:none;}
#myTest ul li{ list-style:none;height:20px;top:0px;}
</style>
<script type="text/javascript">
function scrollUp(){
    var o=document.getElementById("myTest");
    var step=o.getElementsByTagName("ul")[0].getElementsByTagName("li")[0].clientHeight;//获取每次滚动的增量
    o.scrollTop += step;
}
</script>
<div id="myTest">
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
        <li>6</li>
        <li>7</li>
        <li>8</li>
    </ul>
</div>
<input type="button" value="滚动" onclick="scrollUp()"/>