Unreal Tournament Info
The server-only build we're talking about will probably be a lot smaller - as it won't have textures, sounds, or music.
But we want the server admins who get free copies to have the client as well becuase we want them to set the servers up so that they're fun to play, have different map lists, etc, so sending out CDs to them makes sense.
You can also check out this post talking about the HUD, as well as the Unreal Technology page which talks about the Linux port.