Migrate user-data from a non-drupal site I have to migrate 9000 users (name, address, email, tel, photo...) from a non-drupal-site into a new drupal7-site. 

How can I programmatically mimic the registration process and push the data in corresponding fields? And is there a way to change the original password, stored as a MD5-hash, to the drupal7-format while processing the data?

Thanks!
Take a look at the Migrate module.  From the project page:


  The migrate module provides a flexible framework for migrating content
  into Drupal from other sources (e.g., when converting a web site from
  another CMS to Drupal). Out-of-the-box, support for creating core
  Drupal objects such as nodes, users, and comments is included - it can
  easily be extended for migrating other kinds of content. Content is
  imported and rolled back using Drush commands.