How i can integrate phpbb with codeigniter

[eluser]mahmood rehman[/eluser]
i have develop an application in plain php with phpbb integration ,but now i want to integrate the phpbb with codeigniter but it is not working.

Forexample for registration in plain php with phpbb iwrite the code like

$phpbb_root_path = "phpBB3/";
$phpEx = 'php';
require($phpbb_root_path . 'common.' . $phpEx);
require($phpbb_root_path . 'includes/functions_user.' . $phpEx);

$user_row = array(
'username' => $_POST['uname'],
'user_password' => phpbb_hash($_POST['pwd']),
'user_email' => $_POST['email'],
'group_id' => (int) 2,
'user_timezone' => (float) date('now') / 3600,
'user_dst' => date('I'),
'user_lang' => 'en',
'user_type' => 0,
'user_actkey' => '',
'user_ip' => '',
'user_regdate' => time(),
'user_inactive_reason' => 0,
'user_inactive_time' => 0,
);

// Register user...
$user_id = user_add($user_row, false);

but now how i write the same code in codeigniter.how to includes these files.

[eluser]toopay[/eluser]
Include as package? Include in what? Controller? Modules? Oh boy. You really should learn about MVC pattern first.

[eluser]mahmood rehman[/eluser]
i have worked for 6 months in codeigniter but now i am confused how to call the phpbb functions in codeigniter.because for calling their funcions you have to include the root path and include the files.how i include the specific files into codeigniter and use thier funcntions like add user, login etc
thanks in advance