Watching a movie means you have to pay attention for up to 2 hours; if you miss a bit of the action or dialogue, you're going to have a harder time staying interested. So it might be a bit much to aim for right off the bat. Try smaller steps. I used to be a fearful flyer and I had the same problem; even reading a book was a little much for me as the slightest turbulence would break my attention span and I had a hard time getting "wrapped up" in it again.

Try a crossword puzzle or sudouko or a similar distraction before you take a stab at working or movie-watching; it is easy to get really "into" these things, but they can be solved fairly quickly (I can do two moderate puzzles in a 90-minute flight), and if you lose your attention span, it doesn't take very long to get back into it. Or try shorter reading material--- not magazine articles for me as they aren't substantial enough for me to "lose myself" but I love short stories. Bring a laptop with short videos and watch as long as you have the tolerance for, or load them on your iPod. If travelling with a companion, get the travel version of Scrabble or another board game.

It's all about retraining yourself. If you set your expectations too high, you will end up more frustrated than you started but if you fly regularly and take small steps with onboard distractions, you'll get used to paying attention to something (anything!) in flight a lot more quickly than you might imagine!