If you are using PHP, then in the PHP file (note: not just a raw HTML file - unless you've got your server set up to parse HTML as PHP ... and that's a whole separate thread) just add:
<?php
$headerspecific_st = "a tag to tell the included PHP data what file-specific data to display in the header";
include ("C:\wwwroot\lib\header.php"); // abosolute positioning is handled differently on different servers
?>
Your regular HTML page here (obviously, without any header or footer information.
<?php
$footerspecific_st = "a similar tag to tell the included PHP footer what, if any, file-specific data to display in the footer";
include ("c:\wwwroot\lib\footer.php");
?>