did You received similar errors during an PHPBB module install?

Class 'phpbb_db_tools' not found in install.php
include(./includes/db/db_tools.php) [function.include]: failed to open stream: No such file or directory

i found that in my old PHPBB installation i have directory /includes/db/ but in my new PHPBB installation it is not there. So i just copied that folder from old PHPBB files to my new PHPBB installations and Module instalaltion completed successfully.

to download old PHPBB, try http://sourceforge.net/projects/phpbb/files/phpBB%203/