I don't think these 2k movies are intended to be played back in realtime without rendering. I have them, and they are quicktime movies in png format. These movies are best used in a compositor such as after effects, and are usually rendered to a format that will playback in realtime, such as pro res.
FYI I have a 2.66 12 core with 48GB of ram, and they stutter for me too, if I try to play them back in realtime without rendering to a more friendly codec.