怎么在页面上搞一个倒计时？请告诉我原代码

<script LANGUAGE="JavaScript">
<!--
var timerID=null;
function tim(){
var now=new Date ();
var diff;
var righty;
righty=now.getYear();
if (righty<1900)
{righty+=1900;}
diff=Date.UTC(righty,now.getMonth(),now.getDate(),0,0,0)+86400000;
diff1=Date.UTC(righty,now.getMonth(),now.getDate(),now.getHours(),now.getMinutes(),now.getSeconds());
  diff2=Date.UTC(2001,8,19,18,0,0);
diff3=diff1-diff2
if (diff3>0)
{
diff2=Date.UTC(2002,8,19,18,0,0);
}
diff=diff2-diff1
var seconds=Math.floor(diff/1000); 
var days=Math.floor(seconds/86400);
var hrs=Math.floor((seconds-days*86400)/3600)
var mins=Math.floor((seconds-days*86400-hrs*3600)/60)
var sec=Math.floor((seconds-days*86400-hrs*3600-mins*60))
document.all.mxh.innerText="距离我下一个生日还有：" + days+"天"+hrs+"小时"+mins+"分"+sec+"秒"
timerID=setTimeout("tim()",1000);}
function info(){
alert("       您好!   \n\n您不想送我生日礼物吗！\n\n ~o~ 我在等你呢！^_^")
}
document.write("<br><a id=mxh href='http://lucky.myrice.com' onclick='info()'></a>");
tim();
-->
</script>