yep, look at your phpbb config.php find:
$dbname = 'phpbbdb';
$dbuser = 'bbuser';
$dbpasswd = 'bbpassword';
open phpMyAdmin, log in as bbuser , select the database phpbbdb. You have now logged into you mySQL db "as" the phpbb user.
open wp-config.php find:
define('DB_USER', 'wp_user'); // Your MySQL username
back in phpMyAdmin you need to run the command below ...I think the interface changes depending on the version phpMyadmin so I can't be specific where you paste...
GRANT SELECT ON phpbbdb.phpbb_topics TO wp_user@localhost;
Change phpbbdb & wp_user as necessary.