I had much trouble with samba at user level until I realised that the samba
passwords are maintained independently of the unix passwords. The main file
is at /usr/local/private/smbpasswd. You can modify the passwords and add
users with the smbpasswd utility. There is a script which adds unix users as
samba users, but this adds everything (incl daemons etc) and sets the
passwords to X's which disallows access.
Set your passwd with smbpasswd to the same as the windows machine, and it
should work fine.
I still have no way of automatically synchronising unix accounts with samba.