Well, wherever you want the form to be, build it something like this like this(taken from your source):
<form name="login" method="post" action="/forums/login.php">
<br>
<input type="text" name="username" size="25" maxlength="40" value="">
<br>
<input type="password" name="password" size="25" maxlength="32">
<input type="submit" name="login" value="Log in">
</form>
This points it the the forum's login page with the needed variables