Is it a full 90 degrees off? Could this be a setting at the original camera, perhaps it could be re-imported? If QuickTime will show it, you can use Quicktime Pro to rotate it, Someone has mentioned the FinalCut express will rortate the movie, which may give you more options for type of movie file than just QuickTime Pro.
'hayne' has also responded on another thread to your post (Thanks Hayne)
[edited to add part of Haynes comments]