This release is for Drupal 5.x
It is fairly stable, I use it on one of my sites. Please test it and report back if you find any bugs or problems.
UPDATE as of 2007.11.08:
Major update on how protection works. Protected_node now utilises the Node Protection System.
Protected_node now stores passwords as sha1 hashes with optional salt. Salt could be configured in settings.php by definig $protected_node_salt variable with a random value. More entropy means better security. Usage is recommended.