GNU radius using an existing db

Hi all,
I'm trying to use GNU radius with a existing MySQL database, in this
case is vpopmail's database

I'm using this parameters on sqlserver configuration file

# Query to select the password for the given user. Should return one string.
auth_query  select pw_clear_passwd as password from vpopmail where
CONCAT(pw_name,'@',pw_domain)='%u'

# This query returns groups the user belongs to
group_query        select pw_domain as user_group from vpopmail where
CONCAT(pw_name,'@',pw_domain)='%u'

But all I'm getting is this error:

Jul 21 14:55:19 [23608]: (Access-Request local 32
"[email protected]"): Login incorrect
[[email protected]/tatatata]

Should auth_query return some kind of hash instead of a plaintext
password? How could I know what's going wrong?

regards,
-- 
Jordi