Here is written how to set the name of a form with a class:
http://symfony.com/doc/2.0/book/forms.html#creating-form-classes
but how to set the name of this
In version 2.4.1 of Symfony, the solution is:
$form = $this->createFormBuilder ( NULL, array ( 'attr' => array ( 'name' => 'myFormName', 'id' => 'myFormId' ) ) ) ->add (..
You can also set other form attributes this way, but I've not tried. Replace NULL with your data if you want.