I had a flight last September (shortly after 9-11), and found it easiest to run the (unloaded) cameras in their bag through the x-ray, but to ask them to hand-check the film. They weren't happy about it - they tried to tell me that their x-ray machines were safe for any film speeds up to greater than 400, but I insisted (very politely, I might add), so they went ahead and complied. They might tell you that the machines are safe, but you just never know. It's better not to take the chance.
You may want to take all of your film out of the boxes and out of the plastic canisters - you can put the rolls into a clear plastic zip-lock bag. It won't hurt your film (you probably aren't travelling with infrared, now, are you?) and the guys at the security checkpoint may be more inclined to hand-check if they don't have to take too much time to do it. Alternatively, they do sell what are being billed as x-ray proof film bags - I've seen them at my local camera shop, but haven't tried one yet. M Billingslea
