This set of Ruby scripts was used by Songbird to migrate their Drupal 4.5 based blog to Wordpress 2.3. With some modification it could be used by others with similar Drupal and Wordpress versions.

It has support for migrating user accounts, categories, posts and comments. In addition to the database migration, the script generates a set of Apache redirects used to maintain the Drupal URLs for the blog posts, feeds, and categories.