drupal 6 status report, automate via drush?
If you want to use drush, drush -n up will show the available module updates.

Getting the status report (really "requirements" from the API's perspective) is a bit more convoluted, and can be output with

drush php-eval 'include_once DRUPAL_ROOT . "/includes/install.inc"; drupal_load_updates(); print_r(module_invoke_all("requirements", "runtime"))'

Other options are Nagios, Update Status Aggregator, Droptor, or the Acquia Network.