I guess it comes down to what you want to do beyond streaming media really.
One thing that hasn't been mentioned here is that you can't take your 1TB drive and bung it into a NAS, as the NAS would have to initialize the drive which means wiping all the data, so just a little heads up here.
A modern NAS from the likes of Synology, QNAP and Thecus as well as a couple of other companies have easy to configure UI's and some even offer HDMI connectivity so that they can do double duties as media player as well as streamer.
Most also allows you do run a wide range of programs on there ranging from simple media servers to mail servers and wordpress and what not. Sadly a decent NAS doesn't come cheap, as anything with a Marvell processor or similar performs pretty bad when it comes to file copying to/from the NAS itself, despite the NAS having Gigabit Ethernet interface.
Apparently the thing to get is HP's ProLiant MicroServer, as it's got an AMD processor and it looks like a NAS rather than some cheesy second rate PC -
http://h10010.www1.hp.com/wwpc/us/en...009.html?dnr=1