Trying to log user in to vbulletin via PHP

[anneIntegra]

I am trying to make a single login into my web site also log the user in to my vbulletin forum. After I validate my user I set up these REQUEST/POST variables:

$_REQUEST['do'] = 'login';
$_REQUEST['vb_login_username'] = $_POST['username'];
$_REQUEST['s'] = '';
$_REQUEST['vb_login_password'] = '';
$_REQUEST['vb_login_md5password'] = htmlentities(md5($_POST['pass1']));
$_REQUEST['vb_login_md5password_utf'] = md5($_POST['pass1']);

$_POST['do'] = 'login';
$_POST['vb_login_username'] = $_POST['username'];
$_POST['s'] = '';
$_POST['vb_login_password'] = '';
$_POST['vb_login_md5password'] = htmlentities(md5($_POST['pass1']));
$_POST['vb_login_md5password_utf'] = md5($_POST['pass1']);

and then include vbulletin's login.php file to perform the login.

However when I bring up the forum home page, I still have a username and password box waiting to be filled in. Are there cookies or session variables or other things/tricks that need to be set up to have vbulletin think I have actually logged in?

thank you.