I've never been able to get user authentication working in Samba, the documentation and howtos make it seem so easy, yet every time I couldn't get authenticated with the system. In the end I just used the guest settings, but this meant I couldn't write to the shares. Finally today I found the problem while setting up an old PC as a server. Before, the default samba installations were holding the password information in .tdb files (usually in /var/lib/samba). I was trying to change the samba user password using smbpasswd, but couldn't since it kept giving an error. Finally I realised that the passdb setting was wrong, and now it uses the /etc/samba/smbpasswd file instead, which can be modified with the smbpasswd program. Now I'm going to enjoy streaming media over the house, using smb4k to easily mount the shares .
Samba is a great tool, I really like that it performs about 250% faster than a "real" Windows file & print server