[TECK]

You cannot do it with a simple conditional, you need to go the hacker way, that's why you are here at vb.org site.
Here, simple like Bonjour.

/** 
* Checks to see if the IP address of the visiting user is allowed and performs a redirect 
* 
* @param	string	String of allowed IP's 
*/ 
function check_allowed_ip($iplist = '')
{
	global $vbulletin;

	if (empty($iplist))
	{
		return;
	}

	$user_ipaddress = IPADDRESS . '.';
	$addresses = preg_split('#\s+#', $iplist, -1, PREG_SPLIT_NO_EMPTY);
	foreach ($addresses AS $allowed_ip)
	{
		if (strpos($allowed_ip, '*') === false AND $allowed_ip{strlen($allowed_ip) - 1} != '.')
		{
			$allowed_ip .= '.';
		}

		$allowed_ip_regex = str_replace('\*', '(.*)', preg_quote($allowed_ip, '#'));
		// choose where you want to redirect the non-allowed member
		$vbulletin->url = 'forumdisplay.php?' . $vbulletin->session->vars['sessionurl'];
		if (preg_match('#^' . $allowed_ip_regex . '#U', $user_ipaddress))
		{
			// choose where you want to redirect the allowed member
			$vbulletin->url = $vbulletin->options['forumhome'] . '.php?' . $vbulletin->session->vars['sessionurl'];
		}
		eval(print_standard_redirect('redirect_updatethanks'));
	}
}

// separate allowed IP's by a space, you could define a vB option for that 
$allowediplist = '127.0.0.* 127.1.1.53'; 
check_allowed_ip($allowediplist);