PAL and NTSC are different methods of broadcasting. Video files, however, are not broadcasted directly and are therefore neither PAL nor NTSC.
However, some people use the video frame rate to determine whether a certain file would play best on PAL or NTSC equipment. You can find out the frame rate by opening the file in QuickTime Player, then doing a Show Movie Info. PAL is 25 frames per second and NTSC is 29.97.