is there a way to stop movies when going to the next slide?
Yes, you incorporate video player controls into your slideshow "Next" and "Previous" buttons. So the very first thing that happens BEFORE you go to the next slide is that you stop the video player.
Exactly how that is done will depend on what type of video player you are using... FLVPlayback component or NetStream player and exactly how you are controlling the "Next" and "Previous" functions.
But either way, the principle is the same...FIRST control the video player THEN switch to the next image in the slideshow.