The search function in drupal is a bit awkward, although the interface is quite nice. Submissions are not automatically entered in the search database. In version 4.0 you need to revalidate the database which you can do by going to administer drupal -< search and then clicking on reindex all and then clicking on Submit. For version 4.1 there is no search option in the adminstration navigation menu so to reindex the database you have to run the cron.php which you can do by simply typing yourservername/cron.php into your browser. If you have set up the crontab for your drupal site, see here then your database should be updated everytime the crontab is run. This is probably the case if you have set up crontab for version 4.0 as well.

Note that the default search page of drupal is to display the search help above the search box. You can change this behaviour in the above mentioned admistration page.