There are only a few resources on converting / migrating Drupal to WordPress freely. Here are the best free resources according to my personal opinion:
- 2010 -08-05 http://blog.room34.com/archives/4530 by Scott Anderson. This is the oldest resource I can find
- 2010-10-02 http://9seeds.com/news/drupal-to-wordpress-migration/
- 2012-11-30 http://www.allthingscahill.com/2012/11/migration-from-drupal-to-wordpress/ by Mark Cahill
- 2012-02-02 http://fuzzythinking.davidmullens.com/content/moving-from-drupal-7-to-wordpress-3-3/ by David Mullens
- 2013-08-12 https://github.com/robinflyhigh/Drupal2Wordpress , a PHP script by Robin Singh
The most difficult part is reconstructing nested comments. Here are a few resources on arranging nested comments: