Password is not as easy (or possible) as the threads password is done with a one-way MD5 encryption. Which can't be reversed. So if you pulled the password from the DB, it wouldn't match the chat password.
What I do is simply require that they are logged in (which chat does) then their chat name is the same as the username. Passwords aren't needed. I use JPilot, so I don't know how raiderchat does it.
You could create another field in the DB to store the chat password.
