PLace identicle shots on track 1 and 2. Use bezier masking to isolate an element in track 1. Change the track compositing to 3d for both tracks. You can then move either track forward or back (Z axis)which gives the impression of zooming. You can do a pseudo rack focus effect by blurring one track and then by using keyframes bring that track into focus while blurring the other track.
This is just one way of doing this. A more elegant way is to take your scene into photoshop and do the masking or cut out and then cloning a new background where the cut out element had been. A lot more work but muich more believable.