Digital copy PORT file mystery

[Stu123]

When you insert a digital copy into the computer and right click on explore and look in the wmv folder theres 2 versions of the movie on the disc one version around 1.5gb which is obviously the pc version and another one at about 750mb saying PORT which i presume means portable the copy for your ipod.It would be great for disc space on my 8GB ipod if itunes put the correct version on your ipod but when you select sync it insists on always putting the larger file size on.Why is this smaller version of the film just sat on the disc doing nothing if theres no way of getting it on your ipod.Ive tried adding it to itunes libary nothing happens and tried playing it with itunes and it will only play in windows media player.