from what I know, there is usually 2 type of X-ray that airport uses.
One for hand carried luggage - the power of it is usually lower, film with ISO 400 or less should pass through with no notice effect.
Another for checked-in luggage - This one usually higher power, ISO 100 or below should pass through OK.
If u r going to US, there is a even more powerful X-Ray. No film should pass through that. But u must be lucky to get it cos they only does random check for that. Picked by the computer according to the airline staff. I kana on my US trip last yr with my brother's family. Anyway, US custom staff hand checked camera after X-ray too. Just in case that it is a bomb or something disguise as a camera.
If u do not want the film to go through any X-ray at all, u can always keep them in a separate bag and let the custom staff know. Most of them will hand check if u tell them u got film inside.
Just don't put the film into checked luggage and handcarry it. You will be fine. High speed film (think 800 and up) are more sensitive and might be affected, but I have carried 800 speed film before and gone through 4-5 x-rays and it's ok. I routinely carry HP-5 and Tri-X on trips, and they are ok too. Try not to have film inside your camera when going through customs. Sometimes they will ask you to open the film back to check the camera.