I had that problem too with a video I shot in portrait instead of landscape. I thought it would be a simple matter to rotate the clip but in the end couldn't figure out how.
I've since looked into it some more, I found this page ->
http://kingler.net/2005/08/16/19
.. with some tips on how to do it using Windows Movie Maker (if you have WinXP) or using "virtualdub" which apparently you can download. (Link for downloading is on that page).
Haven't yet gotten around to trying it myself but thought you might want to give it a whirl.
Good luck!
And dang man that is a big fish.
