In your /etc/samba/smb.conf (location may vary depending on distro) make sure you have the correct settings:
Code:
[sharename]
browseable = yes
path = /usr/local/your_path
writeable = yes
create mask = 0770
directory mask = 0770
security = share
force group = staff
force create mode = 0770
force directory mode = 0770
This will make sure all ownerships are set to staff and that all files created have permissions 770. Personally I use 775 by YMMV.