mira yo le dejo asi y no me funciona, ¿donde puede estar mal?
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Untitled</title>
</head>
<body>
<form>
<input type="button" value="mostrar" onclick="document.getElementById('oculto').style.d isplay = (this.value == 'mostrar')?'block':'none';this.value=(this.value == 'mostrar')?'Ocultar':'mostrar';">
<table width="80%" border="1" cellpadding="0" cellspacing="0">
<tr>
<td>Primera parte del formulario Nota Empresa</td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<div id="oculto" style="display:none">
<tr>
<td><input type="Text" size="10" value="wqeqweqw"></td>
</tr>
<tr>
<td><input type="Text" size="10" value="wqeqweqw"></td>
</tr>
<tr>
<td><input type="Text" size="10" value="wqeqweqw"></td>
</tr>
</div>
<tr>
<td>Tercera parte del formulario Nota Empresa</td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
<tr>
<td><input type="Text" size="10"></td>
</tr>
</table>
</form>
</body>
</html>