[Aesma Deva]

You could try sending the username and the password to VB's login page, like this:

<form action="http://www.yoursite.com/path_to_forums/login.php" method="post">
<input type="hidden" name="do" value="login" />
<input type="hidden" name="vb_login_md5password" />
<input type="hidden" name="vb_login_md5password_utf" />
Username: <input type="text" name="vb_login_username" /><br />
Password: <input type="password" name="vb_login_password" /><br />
Remember me: <input type="checkbox" name="cookieuser" /><br />
<input type="submit" value="Log in" />
</form>