Webform is a great module to build simple to complex forms for users to fill out, but it has no built-in way to trigger events for Rules. Unfortunately the maintainer is not going to add this kind of functionality anytime in the near future.

Drupal wouldn't be Drupal if you couldn't get around this issue by writing a small module.

The following code triggers an event upon sending the webform, which can be used by Rules. This is useful if you would like to send an email or display a message when the webform is submitted or use any other kind of available action in the system. The current user as well as the webform node and the form data are delivered as a parameter to the executed rule.