PAM authentication

ok - fairly new to postgresql & tring to set up tcp/ip access using pam
authentication
using gentoo_linux 1.4_rc2
postgresql-7.3.1

my pg_hba.conf file has the entries

# TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD

local all all trust
host all all 127.0.0.1 255.255.255.255 trust
host all all 192.168.1.1 255.255.255.0 pam
postgresql

my /etc/pam.d/postgresql file has the entries

#%PAM-1.0

auth required pam_stack.so service=system-auth
account required pam_stack.so service=system-auth

when i try to connect (locally)....
# psql test -U brett
Password: (password entered - i know it is correct)
psql: FATAL: PAM authentication failed for user "brett"

i get the following entries in /var/log/auth.log - and a
Jan 31 16:31:47 achilles unix_chkpwd[25987]: check pass; user unknown
Jan 31 16:31:47 achilles postgresql(pam_unix)[25986]: authentication
failure; logname= uid=70 euid=70 tty= ruser= rhost= user=brett

'brett' has a system level account.
i can connect as user 'brett' if pg_hba.conf is set to 'trust', but never
when pam is involved...

any ideas? i've been mucking around with this for a couple of days & not
getting very far

regards,

brett