Hi Jeff,
One option would be to use the export module and export just the user objects and then import them into the target Kentico instance.
If the passwords are encrypted - there is no way how to get them easily since the hash string salt will be different so it is not possible to decrypt them nor compare. this is better from the security point of view.
If you have stored passwords in plain text, than you can simply get them using SQL query and insert them into the target DB.