If you open up header.php, you can see how the page is displayed based on whether a user is logged in or out:
// START SUBST - <pun_status> if ($pun_user['is_guest']) $tpl_temp = '<div id="brdwelcome" class="inbox">'."\n\t\t\t".'<p>'.$lang_common['Not logged in'].'</p>'."\n\t\t".'</div>'; else { $tpl_temp = '<div id="brdwelcome" class="inbox">'."\n\t\t\t".'<ul class="conl">'."\n\t\t\t\t".'<li>'.$lang_common['Logged in as'].' <strong>'.pun_htmlspecialchars($pun_user['username']).'</strong></li>'."\n\t\t\t\t".'<li>'.$lang_common['Last visit'].': '.format_time($pun_user['last_visit']).'</li>';
You can alter that and add your login forms.
Would I have to call up the header.php file or "include" it? Could someone help me with how to do that ?