Can't make navbar links point to correct location

[testboard]

I'm working on a vBulletin site that is located in a folder called "forum" & I have created a test page like this:
www.domain.com/forum/test/test.php

test.php works as expected when located in the forum folder.
However, I want to make it work from the forum/test/ folder.
I have the following code:

// ####################### SET PHP ENVIRONMENT ###########################
error_reporting(E_ALL & ~E_NOTICE);

// #################### DEFINE IMPORTANT CONSTANTS #######################
define('NO_REGISTER_GLOBALS', 1);
define('THIS_SCRIPT', 'test'); // change this depending on your filename

// ################### PRE-CACHE TEMPLATES AND DATA ######################
$phrasegroups = array('user', 'timezone', 'posting', 'cprofilefield', 'cppermission');

// pre-cache templates used by all actions
$globaltemplates = array(
	'GENERIC_SHELL',
	'navbar',
);

// ######################### REQUIRE BACK-END ############################
chdir('../');
require_once('./global.php');
require_once(DIR . '/includes/functions_user.php');

// #######################################################################
// ######################## START MAIN SCRIPT ############################
// #######################################################################

$out = 'Test.';

// Output page:
$navbits = array(); 
$navbits[$parent] = 'Test';
$navbits = construct_navbits($navbits);
eval('$navbar = "' . fetch_template('navbar') . '";');

eval('$HTML = "' . fetch_template('test') . '";');
eval('print_output("' . fetch_template('GENERIC_SHELL') . '");');

The test template is:

<h3>$out</h3>

My problem is that the navbar does not display graphics correctly & attempts to link to the test folder. E.g. "UserCP" links to "http://www.domain.com/forum/test/usercp.php".

I've tried all sorts of things in the code.
I've checked against other php files & 3rd party applications but I'm now stumped as to what to try next.

Does anyone have any ideas on how I can make the navbar work correctly?
TIA for any advice / ideas?