How do I mute the sound on a movie clip that I'm using in iphoto slide show?

Did your Mac come with iMovie preinstalled?

Then you could export your video, import it to iMovie and remove the audio track. iMovie has two methods to silence a video clip - you can either select the clip in the project and use the command "Detach audio" or chance the audio settings of the clip and set the volume to zero. Then render the video new and import the silent version to iPhoto to use in the slideshow.

Regards

Léonie