Hi, I've just been trying to play Dark Knight in HD through iTunes and there is some lag, like the playback stutters (sound is fine, video stutters). How can I remedy this? Surely the Macbook is capable of playing HD without this lag? I've got a 2.4ghz Aluminum Macbook with 4GB RAM and I'm watching the movie on an LED Cinema Display. I was playing the movie through iTunes with no other programs on, and I'd just logged in to my account (although had not restarted the Notebook for several hours). All help and advice is welcome.