You need to enter the width % for each cell. But wait, there's a better way to do that, it's called CSS:
<style>
.equalDivide tr td { width:25%; }
</style>
<table class="equalDivide" cellpadding="0" cellspacing="0" width="100%" border="0">
<tr>
<td></td>
<td></td>
<td></td>
<td></td>
</tr>
</table>