First of all, let's make clear something. Yes, (unfortunatelly) vBulletin does not allows PHP in templates. But don't stuck on this. Extend your imagination. "If you can't go left, go right. Just don't stand" :)

The solution for this problem is much more easier than you can think. "If you can't add PHP in the templates, add templates to PHP" :) You just need a "echo" command in your PHP file. Yes it's so simple, the result will be exactly what you want, and most important, you can use vboptions, vbphrases, datamanager and everything you want.

1.- Create a template for Header:

<template name="php_header" templatetype="template" date="" username="" version="">
<![CDATA[
{vb:stylevar htmldoctype}
<html xmlns="http://www.w3.org/1999/xhtml" dir="{vb:stylevar textdirection}" lang="{vb:stylevar languagecode}" id="vbulletin_html">
<head>
<title>Your Title</title>
{vb:raw headinclude}
<vb:if condition="$vboptions['storecssasfile']">
{vb:cssfile forumhome.css, options.css, vbcms.css, widgets.css, sidebar.css, forumhome-rollup.css, usercp.css, additional.css}
<vb:else />
{vb:cssfile forumhome.css, options.css, vbcms.css, widgets.css, sidebar.css, forumhome-rollup.css, usercp.css, additional.css}
</vb:if>
</head>
<body>
{vb:raw header}
{vb:raw navbar}
<div class="blockbody">
]]></template>

Remark: If you want to make use of vB sidebar in your page, you must add within head section:

<script type="text/javascript">

</script>
<script type="text/javascript" src="{vb:raw vboptions.bburl}/clientscript/vbulletin-sidebar.js?v={vb:raw vboptions.simpleversion}"></script>

2.- Create a template for Footer:

<template name="php_footer" templatetype="template" date="" username="" version="">
<![CDATA[
</div>
{vb:raw footer}
</body>
</html>
]]></template>

3.- In your PHP file (assuming that is a file which loads all vB functions that you need), add (again is an example):

// Header Block
$templater = vB_Template::create('php_header');
$templater->register_page_templates();
$navbits = construct_navbits(array("my_php_file.php?" . $vbulletin->session->vars['sessionurl'] . ""=> "My Page"));
$navbar = render_navbar_template($navbits);
$templater->register('navbar', $navbar);
$header_block = $templater->render();
echo $header_block;

............Here you can add any PHP code that you like..............

// Footer Block
$templater = vB_Template::create(php_footer');
$templater->register_page_templates();
$footer_block = $templater->render();
echo $footer_block;
As you can see you can use ANY vB template in the PHP file. Just assign it to a variable and then use echo to show it in the screen.

Hope that this short tutorial will be useful to those who have stuck with this vB limitation. I love to use the Smarty template engine with PHP.

That is a way I searched for a lot!
Thanks Nick