Don't think that has much to do with javascript and, there is only one table. It has left and right cells that contain only transparent .gifs but, that sort of layout could even be done without a table. Here's their first row:
HTML Code:
<table cellpadding="0" cellspacing="0" style="width: 100%;"><!-- BEGIN HEADER -->
<tr id="HeaderRow">
<td id="HdrLeft"><img src="image/spacer.gif" alt="" /></td>
<td id="HdrMain">
<div id="HeaderContent"><img src="image/header.jpg" alt="1-800-firedog available at Circuit City" width="975" height="106" border="0" usemap="#headerMap" /></div>
</td>
<td id="HdrRight"><img src="image/spacer.gif" alt="" /></td>
</tr>
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