Yes, track motion.
Set a keyframe for full screen size where you want the change to start. Set a keyframe with the vertical squish a second or so later. Set a keyframe with the horzontal squish a second or so after that.
Season to taste.
Also, at the end, I would add a separate event that is a blurry white circle in the center that fades out over a coule of seconds
Gary Kleiner
Learn Vegas and DVD Architect
http://www.VegasTrainingAndTools.com