Mailchimp Newsletter block position in registration page in Drupal
Ok, you'll need to do this with a custom module and use hook_form_alter and set the weight of the mailchimp list properly.

function MODULE_form_alter(&amp;$form, &amp;$form_state, $form_id)
{
    if ($form_id == "user_register_form")
    {
        //print_r($form);
        //first name field - use proper name
        $form["first_name"]["#weight"]      = 1;
        //last name field - use proper name
        $form["last_name"]["#weight"]       = 2;
        //email field - use proper name
        $form["email"]["#weight"]           = 3;

        $form["mailchimp_lists"]["#weight"] = 4;
    }
}


You should use print_r($form); or drupal_set_message(print_r($form,true)); to inspect the structure of your $form array and get out the proper names of your fields to use in the hook.