I have the HD- and HDR-FOX T2.
The HDR act as both server and client (affected by the 4GB limit streaming bug).
The HD can not act as a server*. The HDR can not serve recordings or media that is stored on an attached USB drive (can only serve media that is on the internal HDD).
*Must test this and confirm, though.
EDIT: Confirmed, there is no Content Share (or FTP server) option in Settings->System->Internet Setting on the HD, and it does not appear on the network.