Yeah you need to be on 5.2 on the ATV 2 to be able to jailbreak it (un-tethered). I know the latest version is 6.0.2, so it's probable you wont be able to jailbreak it unless it's second-hand.
If the OP does pass the requirements then you'll need to jailbreak (The jailbreak is called Seas0nPass) then head over to FireCore's website here. Then run the program aTV Flash (Black), this bit of software costs $29.95 - totally worth it! It makes your Apple TV so much more useful OTB. There are work-arounds i.e apps like AirServer etc which don't require a jailbreak (and they work with the ATV3).
If you are Mac user with an iPhone or iPad you can download (for free) two apps, StreamToMe (for the IOS device) and ServeToMe (for the Mac). Any and all video files that you have on your Mac can be viewed on your ATV3 via AirPlay, works great for me!
The easiest and most reliable way to stream movies that aren't in your iTunes and that aren't in an itunes-friendly file format is with an Mac app called Beamer. You don't need a middleman iPad/iPhone with this. It streams directly from the Mac to the Apple TV. Every file format I've tried so far has worked. I think it was $15, but I've found it to be more reliable than Air Video and Air Play. They have a free trial.
The point is that you don't have to use an iDevice and an app with Air Play. You stream directly to your Apple TV wirelessly.
I have to credit @acosmichippo for that one. He mentioned it here a few weeks ago. I haven't used Air Video since. I watch a lot of movies in segments (over a few days) and Air Video would always crash if I had it paused for an unreasonable length of time. I've had no problems with that happening on Beamer.
Despite the Beamer app's description of using AirPlay to stream content from OSX to ATV, it is really just streaming. According to Apple's web site, AirPlay occurs only between iOS devices and an ATV. There is OSX to ATV AirPlay Mirroring, but Beamer is clearly not doing any mirroring, only simple streaming. Sorry, couldn't help but nitpick a bit.