Login + Cookies on NonVB page

[RiP-Productions]

I searched this site for some questions, but couldn't find the complete answer. That's why this post

I have a news page containing news about the world where members (which have their account registered on the Vbulletin database) can post reactions on the news. So members who are registered on the forum can post reactions on the news page (nonvbulletin).

I can read the cookies from the forum (are set on domain and not on domain/forum directory).

I read cookies like follow

PHP Code:

<? 
if ($bbuserinfo['userid']!=0) { 
    $username=$bbuserinfo['username']; 
    echo "Welcome back <b>$username</b>,<br><br>"; 
} 
else { 
    echo "Welcome <b>guest</b>,<br><br>//LOGIN BOX"; 
} 
?>

Now is my question how do I get with the else (see LOGIN BOX a login box (using a form) to let the user login and use the function vbsetcookie (or other way to set the cookie) for the user.