That’s a big system for just a file server.
Usually file servers require little memory and cpu, but lots of bandwith (1Gb network) and disk space (2TB or so).
I recommend FreeNAS, because of its multitude of built in protocols.
FreeNAS is an embedded open source NAS (Network-Attached Storage) distribution based on FreeBSD, supporting the following protocols: CIFS (samba), FTP, NFS, TFTP, AFP, RSYNC, Unison, iSCSI (initiator and target) and UPnP.
It supports Software RAID (0,1,5), ZFS, disk encryption, S.M.A.R.T/email monitoring with a WEB configuration interface (from m0n0wall).
FreeNAS can be installed on Compact Flash/USB key, hard drive or booted from LiveCD.