[Samba] sync samba and unix passwords

[Damien]

Hi,

I've samba version 3.0.14a-debian installed, and I try to enabled the 
password synchronization between samba and linux.
What I want to do (correct me if I made a mistake and this is not 
possible) : when I change a password (logged as root) for a samba user 
(by smbpasswd), I would like the change to be done for the unix account.
I've tried differents configurations of smb.conf, with no success.
Here is an extract of my smb.conf :

   security = user
   encrypt passwords = true
   passdb backend = tdbsam guest
   obey pam restrictions = yes
   invalid users = root
   unix password sync = yes
   passwd program = /usr/bin/passwd %u
   passwd chat = *Enter\snew\sUNIX\spassword:* %n\n *Retype\snew\sUNIX\spassword:* %n\n .
   passwd chat debug = yes
   log level = 100
   pam password change = yes

If someone could help me to solve this problem, it will be a good thing 
for me.
And next, is it possible to do te reverse thing : when I change an 
account password (by passwd, as root), the change take effect for samba 
? And if it is, could you say me how to proceed ?

Thanks
Damien