Quicktime movies playing on Ubuntu Linux that do not play on Windows XP

This is odd: I installed the latest Windows XP Quicktime from Apple and hi-res movies that I exported from iMovie on my Mac will not play, but play fine on Ubuntu (I did run "Alacarte" when I first installed to get some 3rd party multimedia support). I have a shared FAT32 partition, so I was running against the same files on Windows XP and Ubuntu.