Windows Photo Gallery - Slide Show

Could anyone advise please how to change the default settings when playing a
slide show using Windows Vista Photo Gallery. I am playing a mixture of video
clips and still photos and the slide show moves to the next shot before the
video clip has finished playing. I would like to extend the time that each
separate clip is presented for or, better still, have ithe timing set so that
Photo Gallery moves on after each video clip has finished.

Many thanks