What exactly are you trying to do? I'm asking because I think you're getting confused.
The PasswordValidator class is only used to verify that when users change their password, the new password complies with certain rules defined there. The validator class is *not* used to authenticate users.
If you want to authenticate users against some other data source, you should use a custom user data provider. You can always copy the default LifetypeUserDataProvider (which ensures that you will still use LT's default user tables) class and make your customizations wherever necessary. The method names in that class are pretty self-describing so you should have no problem finding the right place to make your changes.
The functionality of user data providers is described here:
And the documentation related to how to create new providers is here:
http://wiki.lifetype.net/index.php/Deve ... _Providers