Question about PIP on Sony Vegas Pro 10

Okay so i'm making a video, and right now I have a clip running in whole screen, and then my PIP clip is in the bottom left corner of the screen. I'm trying to take the clip in the bottom left (the PIP) and make it Pan, or expand, to take up the whole screen, but I cant seem to find out how to do it. I've tried going back to "Track Motion" and using keyframes and moving it, but the box stays stationary and wont move. Any tips, or any video explaining what i'm trying? Thanks tons.