Rotating video clips in iPhoto

I have one or two small video clips in iPhoto 11 (9.4.2), which were shot in portrait mode with a standard digital camera. They appear in iPhoto sideways, but it seems that the iPhoto editing tools will not allow me to rotate them. I need to put one of these into an iDVD slideshow I am creating, and I certainly don't want it sideways.

What is the easiest way to rotate such video clips?