prova cosi:
codice:
<script language="JavaScript" type="text/javascript">
<!--
function frase1() {
document.getElementById('NomeTexArea').value="prima frase";
window.setTimeout("frase2()", 1000);
}

function frase2() {
document.getElementById('NomeTexArea').value="seconda frase";
}

timeoutId=window.setTimeout("frase1()", 1000);
//-->
</script>
</head>
<body>
<div id="contenitore"><textarea name="NomeTexArea" id="NomeTexArea" cols="20" rows="5">qui andra la frase</textarea></div>