Adding Fade In Steps From One To Another Keyframe?

I am making a comic in Flash CS4 using AS2 and I'm trying to figure out how to add a quick crossfade from one keyframe to the next. When the user presses the "next" button, I want the current image to fade down and the next image to fade up. The images are arranged so the heads and text are positioned to the left and right, so as one head fades up the other would fade down, see picture below. It's a conversation.

I understand how to do it if the scene plays automatically, but I want it to stop on each keyframe so the user can take their own time to read the text. I'm just starting out and used another tutorial to come up with the AS that is controlling it now. That AS was written when all the keyframes were in a row next to each other. Now I've adding some blank frames between them to create space for the Tweens, but I don't know how to modify the AS so it steps from keyframe to keyframe. It's still stepping though one frame at a time.