<html>
<head>



<script language="JavaScript">
function rechne()
{
text1=document.getElementById('tf1').value;
zahl1=parseFloat(text1);

text2=document.getElementById('tf2').value;
zahl2=parseFloat(text2);

summe=zahl1+zahl2;

document.getElementById('ergebnis').innerHTML = summe;
}

function taste(e)
{
  if (e.keyCode == 13) // RETURN-Taste
  {
     rechne();
  }
}
</script>

</head>
<body>
<div style="position:absolute; top:10px; left:20px; width:350; height:100px; background-color:red;">
<h2>Summe</h2>
<form>
1. Wert: <input type="text" id="tf1" size="5" maxlength="10" onKeyPress="taste(event)">
2. Wert: <input type="text" id="tf2" size="5" maxlength="10" onKeyPress="taste(event)">
<input type="button" name="knopf" value="Aktion" onClick="rechne()">
</form>
</div>
<div id="ergebnis" style="position:absolute; top:150px; left:120px; width:80px; height:20; background-color:yellow;">
</div>

</body>
</html>