How to setup Samba shares to only be accessed by certain users?

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http://askubuntu.com – I have a RAID10 array mounted on Ubuntu Server 12.04. I have created a few folders within the mount point and want the following functionality. There will be 4 users, 3 of them are windows users: 'one' 'two' & 'three'. 'four' is a media streamer that only needs to access the MEDIA share. One Two and Three need to have full access to the media share and their own personal shares (for documents) which no other users but them can access. Currently, User Four works perfectly (Has full access to the MEDIA folder and can't access folders owned by other users). The problem is, when logged in as (HowTos)