includes no html com php

boas.

tou a fazer o meu 1º site com um sistema de templates. mas tou com um problema, preciso de fazer um include dentro de um arquivo .html.

o codigo k tou a usar é:

template.php

<?php
class BasicTemplateSystem {

	var $template_html = array();
	var $template_vars = array();
	var $template_path;

	// --------------------------------------------------
	// Load template html files into variables
	// --------------------------------------------------
	function TemplateLoad($template) {

 // Goes through every template and loads it
 foreach ($template as $index => $value) {

 // Just load the template or check if we should load it?
 if (is_array($value)) {
 foreach ($value as $file => $load) {

 // Should we load this template?
 if ($load) {
 $this -> template_html[$index] = file_get_contents($this->template_path.$file);
 }
 }
 } else {
 $this -> template_html[$index] = file_get_contents($this-> template_path.$value);
 }
 }
	}

	// --------------------------------------------------
	// Define template content for some	references
	// --------------------------------------------------
	function TemplateDefine($references) {

 // Clears the current references and their content
 $this->template_vars = array();

 // Saves the content with it's reference associated
 foreach ($references as $reference => $content) {
 $this->	template_vars['{'.$reference.'}'] =	$content;
 }
	}

	// --------------------------------------------------
	// Replace references in template with saved content
	// --------------------------------------------------
	function TemplateExport($template,$getonly = false) {

 // Should we parse the tempalte references or just get the html?
 if (!$getonly) {

 // Split the html code into lines
 $html_code = $this->template_html[$template];
 $html_code = explode("\n", $html_code);
 $line_count = count($html_code);

 // Replace only the lines needed
 for ($i = 0; $i < $line_count; $i++) {
 foreach ($this->template_vars as $reference =>$content) {
 if (strstr($html_code[$i], $reference)) {
 $html_code[$i] = str_replace($reference, $content, $html_code[$i]);
 }
 }
 }

 // Join the html code lines and	return the final code
 $html_code = implode("\n", $html_code);

 } else {
 $html_code = $this->template_html[$template];
 }

 // Return our template html code
 return $html_code;
	}
}
?>

index.php

<?php
	include('functions/functions_template.php');
	$BTS = New BasicTemplateSystem();
	//chama temnplates
	$BTS-> TemplateLoad(array(
 'header' => "styles/AnimeLand/template/overall_header.html",
 'footer' => "styles/AnimeLand/template/overall_footer.html",
	));

	//define tags a substituir
	$BTS->TemplateDefine(array(
 'T_THEME_PATH' => "styles/AnimeLand/theme",
 'TITLE' => "AnimeLand",
	));

	echo $BTS-> TemplateExport('header') . $BTS-> TemplateExport('footer');
?>

eu precisava de fazer um include de um .html dentro do overall_header.html.

o phpBB3 utiliza "<!-- INCLUDE menu.html -->, <!-- IF menu -->", <!-- ENDIF -->

alguem sabe como fazer isto?