For adding any template page in symfony, add your template to apps/appName/modules/urModule/templates/ dir. Name it like listSuccess.php. Now for accessing this page from browser, you need to associate this page from an action. Define an action for this page. As you named your page like listSuccess.php, you need to create an action (method) in your modules actions/actions.class.php with name executeList(). In this executeList() method of urModuleActions class, you need to return sfView::SUCCESS.
SfView::SUCCESS is default return value from actions method. Create your page with name listError.php and return sfView::ERROR from method.