When you have a user in 'admin users', samba will always do file operations for this user as 'root', even if 'force user' has been set.

Newer windows clients(NT4, 2000, XP) send encrypted passwords. Samba can't compare these passwords to the unix password database, so it needs it's own user database. You can add users to this database using "smbpasswd -a user-name".

See also the "User database" chapter of the samba HOWTO Collection.

By default Samba uses a blank scope ID. This means all your windows boxes must also have a blank scope ID. If you really want to use a non-blank scope ID then you will need to use the 'netbios scope' smb.conf option. All your PCs will need to have the same setting for this to work. Scope ID's are not recommended.