tuxbliki/app/views/sessions/new.html.erb

<%= form :action => url(:sessions) do -%>
  <fieldset>
    <legend>Login</legend>
    <p><%= text_field :name => :username, :label => 'Username: ', :id => 'username' -%></p>
    <p><%= password_field :name => :password, :label => 'Password: ' -%></p>
  </fieldset>
  <p><%= submit 'Login' -%></p>
<% end =%>

<script type="text/javascript">
  $('username').focus();
</script>