HELP! Playback motion not smooth

I'm still kind of new with Vegas 8 movie studio. Window's Movie Maker was a cakewalk. Here's what I'm doing. I'm making a "part two" to a Harry Potter music video that I made with WMM. So I'm using several clips from the movies. However, when I play it back, the motion isn't smooth. The video will occasionally hang in places as the audio continues as it should. I thought maybe it was from zooming in and out so much to apply my clips and FX affects so I tried saving it, then reopening it again. Still does the same thing, and not always on the same clips.

Is there another setting I should be applying for smooth motion, instead of it looking choppy? Do I have to apply such a feature to each clip, or can I apply it to the whole track?