Det er ret nemt med java script:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"
http://www.w3.org/TR/html4/loose.dtd"><HTML>
<HEAD>
<TITLE>Tomt dokument</TITLE>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<SCRIPT LANGUAGE="javascript" TYPE="text/javascript">
var x = new Date().getTime();
function opdaterTid(){
var nytid = new Date().getTime();
document.getElementById('minDiv').innerHTML=Math.floor((nytid-x)/1000)+' s.'
}
</SCRIPT>
</HEAD>
<BODY ONRESIZE ONLOAD="setInterval('opdaterTid()',1000)">
<BR>
<FORM ID="minForm" NAME="minForm">
<INPUT ID="minInput" NAME="minInput" TYPE="text" VALUE="Tom" ONFOCUS="if(this.value==this.defaultValue)this.value='';" ONBLUR="if(this.value=='')this.value=this.defaultValue;" NAME="minInput" ID="minInput" SIZE="20">
<BR>
<button name="button1" id="button1" onmouseover="this.form.button2.style.display='block';" onclick="location.href='enAndenSide.html';">Mus over og tryk!</button><br><br>
<button name="button2" id="button2" style="display:none;">En ny knap!</button>
</FORM>
<BR>
<BR>
Du har nu været her: <DIV ID="minDiv">En div-tekst</DIV>
<SPAN ID="minSpan">En span-tekst</SPAN>
</BODY>
</HTML>