Otra forma (más simple, creo):
Código HTML:
<head>
<script type="text/javascript">
function muestra2()
{
var celdas = document.getElementsByTagName("td")
for (i=0; i<celdas.length; i++)
{
if ( celdas[i].className=="oculta" ) celdas[i].className="mostrada"
else if ( celdas[i].className=="mostrada" ) celdas[i].className="oculta"
}
}
</script>
<style type="text/css">
<!--
.oculta { visibility: hidden; }
.mostrada { visibility: visible; }
-->
</style>
</head>
<body>
<table border="1" cellspacing="4">
<tr>
<td>A</td>
<td>B</td>
<td>C</td>
<td class="oculta">D</td>
<td class="oculta">E</td>
</tr>
<tr>
<td>10</td>
<td>20</td>
<td>30</td>
<td class="oculta">40</td>
<td class="oculta">50</td>
</tr>
<tr>
<td>11</td>
<td>21</td>
<td>31</td>
<td class="oculta">41</td>
<td class="oculta">51</td>
</tr>
</table>
<a href="javascript:muestra2()">mostrar/ocultar columnas</a>
</body>