Do you want a full CMS/Intranet solution a-la sharepoint, or could you slap a bunch of drives into a tower, stick a copy of something like FreeNAS onto the system, and add a VPN for anyone who needs access to the share points remotely?
Basically, what exactly are you looking for in your file sharing capabilities? TruCrypy? Torrent Server? Literally-LAN based storage for a corporate network?