Well now you know how certain sections of code would fall into a page, you could make an index that calls the includes where you need them, since the header and footer can both be one table unto them selves you might include the header firs then in the index using either HTML or echo the tags for php you would start a new table with three big cells (td tags or table data) all within one table row so after you included the header into your page you would have some code like;
?><table border=? cellpadding=? cellspacing=?><tr>
<?
include("left.php")://set the <td width=to a percentage in these includes
include("content.php");//like left <td width=20%><td width=60%><td width=20%>
include(right.php")//this way it will fit all browsers screen and lay out like you wish.
?></tr></table>
<?
include("footer");
?>
Each included file (left.php, content.php, right.php would start with a <td> and close with a</td> Everything in between you would just write like it were regular HTML. The table would close before you include the footer with a </tr></table> as shown in the code above. So it would take a little work and learning a little about CSS might help to use with all you add to the site. You could nest tables within the individual files either by writing them as part of the file or including other files where you need them, just look at an include file as hey I want to put this content right here.