Yeah, sorry thats Z-Index I always make that mistake...

You could put the body content of the document in an external file (just the body content still though because you'll end up with two <head> and <body>) and use a ssi to read the content.

<td id="atd">
<!--#include file="include.htm" -->
</td>

Or you could set the content using document.getElementById('atd').innerHTML and have the content in an external js file.

I'd use the first idea because you don't have to mess with javascript BUT if this is for an online site then make sure the host supports SSI.