firewall/router with vpn client support. This allows for a vpn client to be installed and used on the remote desktops for secure communication with your server.
You don't need server to share a drive. Get a NAS unit. Mirrored gig drives should do you or go larger. Cheaper than server OS and its hardware.
Office workstation should have a dvd dl burner so you can backup the data on the NAS unit.