Yes, you can stream from a freeNAS to something like the WD TV Live.
Currently the only real media streamers out there that support local streaming are
WD TV Live
Seagate Free Agent line (most/all of which is now discontinued?)
Apple TV, with caveat
That is, pre-packaged deals. You can load up XBMC on a lot of hardware, and Rapsberry Pis are an excellent choice for this, but it involves at least a fair amount more user technical experience and DIY work to get running.
Or, well, your average computer you can stream to as a Home Theater PC (HTPC).
Trust me, I've been looking in to it a lot. I have a couple of Seagate Free Agent Theater + streamers, that worked fine for awhile, but the Netflix app on them are badly out of date and I think the whole Seagate line got EOL about 12 months ago, at least the Theater + haven't had support in >>>12 months now (last firmware update, with some bad bugs, was around 18 months ago 2.23, so I am on the one prior, 2.20).
One of mine just stopped working to stream from my server. Randomly it refuses to connect. It'll connect to a USB drive off my router, but it takes AGES to connect (about 60s, compared to the still working ones 1-2s to login).
The Apple TV is nice, especially if you like Apple, but it requires iTunes to stream locally, which is really annoying is there is a lot more "upkeep" requires for movies in iTunes than simply pointing something at your existing folder structure to stream moves using CIFS/SMB, which is what I do now.
The dead Seagate is getting replaced, when it shows up, by an Apple TV. I don't like the added upkeep of iTunes, but whatever. My file server can run iTunes just fine, and admittedly its only maybe an afternoon of work to import my existing collection of 800+/- movies in to an iTunes library and tag it all so that I can sort it properly on an Apple TV for view. The TV shows are going to be more work to manually go in an add season and episode numbers, but whatever. Again, the whole thing is an afternoon of work and then its only an extra minute or two of manual work a week in the future as I add movies (my collection grows maybe 1-2 movies a week, rip, transcode and currently my desktop autobacks up to the server weekly at night, but now I'll also then need to manually add the files to iTunes on the server and tag them before they'll show up on an Apple TV).
For network setup, whatever works best for you. 802.11g can stream HD movies just fine, so long as you don't have too many clients hitting the network at once and/or too much congestion from neighbors or too far from your router. a decent 720p movie tends to be 4-7Mbps and a decent 1080p movie is around 6-12Mbps. 802.11g on a bad day is around 10-15Mbps and on a good day we are talking 30Mbps usable, so if you don't have neighbor interferance, 802.11g should be fine for at least a couple of resonable 1080p bitrate streams.
It won't handle raw Bluray, but how many people stream that?
802.11n, 150Mbps will handle raw Bluray just fine, again, so long as you don't have much mussing up your wifi network.
Me personally, I hardwire everything I can. My wired network is limited to 2,000Mbps in traffic to my server, minus TCP/IP or UDP overhead, which is very limited, my wireless network is limited to 300+150Mbps minus protocol overhead, attenuation, etc all of which can be a lot (my router is on Channel 1, 20MHz and my AP is on Channel 6+11 40MHz, so no shared wireless). Only thing that is wireless are things that actually get carried around.
