Yep, it is AirFlick, my mistake.
Here's a quick guide:
Download and install Air Video Server and add your shared folders. You will need to enable "access from internet" under the remote settings in preferences and get the server pin. You can add a password but it is not necessary.
Once this is set up open up airflick and you'll see a little arrow pointing up labeled "AirVideo Access" in the main window above the play and stop buttons. Click it to open up the side drawer. The drawer then asks for the pin that was given to you earlier and type in your password if you chose one. The window should populate with a directory of your shared folders so just choose your video and it should be streamed to your AppleTV.
Airflick works on 4.3. I'm using it now.
I was using xmbc for awhile but I felt it slow and buggy and if I tried to play an mkv it would always stutter after about 30 seconds. For this set up I just convert to mp4 using mkvtools and stream with airflick. I know it's one more step but it doesn't stutter.
Also I found my appletv to be less stable with the jailbreak. That and the fact I wanted to use nba league pass, if just for the highlights.
I also tend to send a lot of one off videos and pictures that I'm working on to see how they look on my 40" tv as opposed to my 13" macbook.
Hope this helped.