existing users

Hi every one,
Is there any body that knows, how I can import my existing Drupal users into PHPBB3?!
My Drupal site have over 800 users, and I install the PHPBB3 by arkepp guide.
Every thing is OK, it means that new user can register and PHPBB3 is recognising them! But my existing user can not login to PHPBB3!
How i can fix this problem!? Please help me!

i'm working on a replacement site using Drupal and phpBB3. I already have a phpBB3 forum up and running, and have around 27500 posts and over 1300 users.

I've managed to install the phpBB module, and get users to be able to log in, and post, play around etc.

I know this isnt production ready yet, and i'm just playing around, but how would I go about inserting all my existing data into this bridge? db backup and then upload it?