Código PHP:
<HTML>
<HEAD>
<TITLE> Foro</TITLE>
</HEAD>
<BODY>
<script type="text/javascript">
function send(by, tosend, win) {
var to=document.getElementById(tosend);
var win=document.getElementById(win);
win.innerHTML+=by+': '+to.value+'\n';
to.value=''; to.focus();
}
</script>
<style type="text/css">
label {display:block}
</style>
</head>
<body>
<div>
<textarea id="win" cols="60" rows="6"></textarea>
<input id="tosend" type="text" style="width: 437px;">
<input type="button" value="Enviar" onclick="send('Fernando', 'tosend', 'win');">
</div>
</form>
</body>
</html>