Hello,
I have a solution for your HD movies and the fact you want to stream them from an ext hard-drive to ATV2...
Originally I wanted to do the same thing as you, have the TC as a storage device for my music and movies so I did exactly what you are doing (or have done!) and it worked fine for about a month then the whole drive crashed and I lost EVERYTHING. I would not recommend using TC as a storage device!
I figured there has to be a way for ATV to speak to an external drive and there is, through the TC on a jailbroken ATV with XBMC on it. So I then jailbroke the ATV2. I then connected my ATV2 via ethernet to my TC, and then my TC via USB to a 4TB external hard-drive with all my media on it. XMBC then picked up my TC and external hard-drive and I stream HD movies to it and it works like a dream. ATV2 must be connected by ethernet though to stream HD without a jitter. (Computer is not on for this). So, for movies this is the best solution I have and the user-interface on XMBC is gorgeous with really nice art-work and it is simple to use. Music on XMBC however is not working....yet.
Anyways just thought that might help but I'm afraid purchasing TC as a storage device was probably not the right thing to do, I learnt the hard way....