Implement PunBB into my Site[How to]

Hello all,

I've been strugling around in the codes of PunBB but it doesnt look that i can fix this on my self.

I run a community site at this moment and i like to use the PunBB as a BB. But it can;t be that the users have to log in for 2 times if they like to use the BB. Wich steps have i to make to implement my PunBB into my site.

To help the experts over here i have some code pasted under here (the name of the cookie etc aren't the real).
( i think that that is the biggest deal.. The cookie etc.)

So can you help me?

The code:

<?php

if(loggedin( ) == false) {
   ?>
<script language="javascript">
window.defaultStatus = "Loggedout.";
</script>
<style type="text/css" media="screen">
    @import url("./ph.css");
</style>
      <div class="menu_txt">
         <form name="login" action="leden/login.php" method="post">
         Username:<br>
         <input type="text" SIZE="12" class="input" value="" name="username" onFocus="clearThis(' Username',this)" onBlur="fillThis(' Loginnaam',this)"><br>
         Password:<br>
         <input type="password" SIZE="12" class="input" value="" name="password" onFocus="clearThis(' Password',this)" onBlur="fillThis(' Password',this)"><br>
         <input type="submit" class="submit" value=" LOGIN! " style="color: black;"><br>
         </form>
      </div>
   </div>
   <?
}

And the cookie stuff

## Database connection ##

$db['connect'] = mysql_connect( $config['db']['host'], $config['db']['user'], $config['db']['pass'] );
if( mysql_select_db( $config['db']['base'], $db['connect'] ) == false ) {
        print $lang['db']['error'];
        exit( );
}

define( 'pad', 'somewhere.com', true ); //Website path
define( 'url', $Site[ 'base_url' ], true ); //Website adres

require pad . 'include/functions.php';
$_SESSION['ip']  = client_ip( );
require pad . 'include/ubb.php';
require pad . 'include/online.class.php';
if( ingelogd( ) ) {
    $Query = mysql_query( "SELECT * FROM leden WHERE Id = '" . $_SESSION['id'] . "' " );
    $user = mysql_fetch_assoc( $Query );
   
    setcookie( '2609198787190926', $_SESSION['username'] . '(24124546512154)' . $_SESSION['id'], time( ) + ( 60 * 60 * 24 * 365 ) );
}
else{
    $user = array( );
    if( isset( $_COOKIE['2609198787190926'] ) ) {
        $EX = explode( '(24124546512154)', $_COOKIE['2609198787190926'] );
        $_SESSION['username']        =    $EX[0];
        $_SESSION['id']                    =    $EX[1];
        header( 'Location: ' . $_SERVER['PHP_SELF'] );
    }
}

?>

Thanks!