Append checkbox to password input

Created by: goshacmd

When I write, for example

<label for="user[password]">Password</label>
  <div class="input">
    <div class="input-append">
      <input class="xlarge" id="user[password]" name="user[password]" type="password">
      <label class="add-on">
        <input type="checkbox">
      </label>
  </div>
</div>

Why checkbox is not appended to input field? http://d.pr/FvnD+ I need it to use only one password field on sign up, when checkbox is checked, password is shown.