Thanks for trying, sorry you had problems.
The password issue shouldn't be happening. How are these users registering? Is it through the normal wordpress registration page, or a plugin?
After registering but before logging in, are you able to confirm if that user exists in the phpBB database? If so, is the password hash comparable with the WordPress one? If you don't know how to check this, then never mind...
For the second issue, you probably have "automatically create users in phpBB" turned on. That's fine and will work, but before you turn it on, you have to map together users that already exist in both phpBB and WordPress. For example, if user "Jhong" already exists in phpBB, but isn't mapped to the WordPress user account "Jhong", then when that user logs in, they will be given an auto-created account in phpBB. Since "Jhong" already exists, that new user will be "Jhong1". (All of this is transparent to the end user -- they just see they are logged in).
To solve the problem, temporarily turn off the phpBB auto-create option and visit the user mapper. Clean up any incorrect mappings, deleting the appropriate duplicated users. Then map together any users that exist in both phpBB & WordPress. When done, and everything looks tidy, you can re-enable the auto-create option.
Let me know if you have any other problems. There are a few bugs in v0.9.1.6 that are fixed in the currently nightly packages at wp-united.com.