<form action="http://your.moodle.net/moodle/login/index.php" method="post" name="form" id="form">
<p><input type="text" name="username" size="15" /></p>
<p><input type="password" name="password" size="15" /></p>
<p><input type="submit" name="Submit" value="Login" /></p>
</form>
Gustav was right but for me worked without moodle, like this:
<form action="http://your.moodle.net/login/index.php" method="post" name="form" id="form">
<p><input type="text" name="username" size="15" /></p>
<p><input type="password" name="password" size="15" /></p>
<p><input type="submit" name="Submit" value="Login" /></p>
</form>