Interesting comment. I had that issue on my Mac, when I imported video from my old HTC PPC-6800. I think there was a Codecs issue, if I remember correctly.
I also noticed that there were issues between filenames called MP4, or M4P... not sure if this is the same kind of thing, though.
What I did was choose different programs to open those files. For instance, Quicktime never did open some files correctly, and I used a host of others MPlayer for one, but that was for my Mac. Not sure how to advise you since I'm a novice with Droid, and I have not even tried this yet.
Edited: I messed up on my details. I ran into issues when I moved old video from my Cingular 8125 to my Mac, and then when I used the PPC 6800 also on my Mac. I was using a Windows Mobile file on a Mac, and it did create problems (video, once from portrait -> landscape, flipped back, and when there was sound on the mobile phone, there was none on my Mac - until I used a third-party program).