samba - Aug 2009 - Users created by smbpasswd not a member of any ntgroup

Hi Guys,

Ubuntu 8.04 Server 64-bit Edition
Samba 3.0.28a

I have configured samba as a PDC with winbind. I DO NOT have a windows
NT server on the network, but i need winbind for squid and other
purposes.

root at sunbox:/usr/lib/squid# net rpc group list
Password:
Domain Users
Domain Admins
Administrators
Users

My question is, if we configured samba as a PDC, when users are
created using smbpasswd command, the users  should be a member of one
of the above groups right? But, when i checked,

#net rpc user info user1 -Uroot%secret
None

Is this by default and should i add all samba users to windows groups
manually??
How does this work?

Thanks
Avinash