How many users is this for? How do they authenticate now? There is a mysqlsam backend mentioned in "Samba-3 Official HOWTO & Reference Guide" but no further information on it that I could find in the book. I'd recommend that book and "Samba-3 by Example". They are available in the book stores, or you can download the pdfs from the Samba website. Also, most distro's have a `samba-doc' package that has these two books.
I don't think you are approaching this the correct way. There are different password backends for samba. They contain more information than the the username and encrypted password. You can use the smbpasswd command to add users & passwords. There is also a tdbsam database which you might want to use for over 20 users. Or you can use ldap or AD to handle authentication. The two books I mentioned have step by step instructions, including setting up the directories to share, and their permissions.
A samba user needs to be a Linux user as well. A user will have a UID on Linux as well. That is what the Linux permission system is based on.
Take a look at these two share definitions:
comment = Network Profiles Service
path = %H
read only = No
store dos attributes = Yes
create mask = 0600
directory mask = 0700
comment = All users
path = /home
read only = No
inherit acls = Yes
veto files = /aquota.user/groups/shares/
The profile share will show up as profiles in explorer. When a user clicks on it, they will need to authenticate if they haven't started a session. When they do, they will see their own share. The other users shares don't even show up.
The `users' share will show up as `users' in explorer. When a user opens it, they will see a share by all of the users and will need to locate their own share and open it. Access to the other shares depends on the permissions of each users home directory.