entre a tag <HEAD> coloque isso:

<SCRIPT language="JavaScript">
<!--
function startclock()
{
var thetime=new Date();

var nhours=thetime.getHours();
var nmins=thetime.getMinutes();
var nsecn=thetime.getSeconds();
var nday=thetime.getDay();
var nmonth=thetime.getMonth();
var ntoday=thetime.getDate();
var nyear=thetime.getYear();
var AorP=" ";

if (nhours>=12)
    AorP="P.M.";
else
    AorP="A.M.";

if (nhours>=13)
    nhours-=12;

if (nsecn<10)
 nsecn="0"+nsecn;

if (nmins<10)
 nmins="0"+nmins;

if (nday==0)
  nday="Domingo";
if (nday==1)
  nday="Segunda-Feira";
if (nday==2)
  nday="Tera-Feira";
if (nday==3)
  nday="Quarta-Feira";
if (nday==4)
  nday="Quinta-Feira";
if (nday==5)
  nday="Sexta-Feira";
if (nday==6)
  nday="Sbado";

nmonth+=1;

if (nyear<=99)
  nyear= "19"+nyear;

if ((nyear>99) && (nyear<2000))
 nyear+=1900;

document.clockform.clockspot.value=nhours+": "+nmins+": "+nsecn+" "+AorP+" "+nday+", "+ntoday+"/"+nmonth+"/"+nyear;
setTimeout('startclock()',1000);
}  
//--></SCRIPT>


na tag <BODY> coloque:

<SCRIPT language="JavaScript">
<!--
startclock();
//-->
</SCRIPT>