I've got a desktop PC in one room.

In another room, I have a laptop which I've got connected to a TV via a HDMI cable.

I want to be able to store movies on a nutural device which can be accessed by either at anytime.  

For example, If they're on my PC it needs to be on to watch them on the laptop/tv and I don't want to have to copy them across each time. I could use an external drive but looking at a disk or something which can be connected via cat5 cable maybe

Is there something I could do?