Linux file server for an inexperienced admin
Solution 1:
Entry-level solutions are Samba and FreeNAS. If you are not comfortable with looking after a *nix server, and given the low number of users, stick to FreeNAS.
Solution 2:
SME server. Free, ready out of the box, just install. Uses a web interface. It rocks.
http://wiki.contribs.org/SME_Server:About