In short, you'll want to hook into the interaction events fired by the Cover Flow object when manipulated by the user.
Each interaction fires an event. To see the possible events, select the Cover Flow and click the code button and you'll see the events you can intercept in the "Add Event Handler" drop-down menu including:
- Did Tap Front Cell
- Did Select Cell
- Did Focus Cell
- Did Begin Swipe
- Did End Swipe
Showing a zoomed version of the center (focused) cell will vary based on how you want to present the focused content.
If you want to zoom the focused cell full screen, you can have an offscreen Image View object that you'll display when the appropriate event is triggered and set the image property of the Image View to that same image in the focused Cover Flow cell.
You'll then add a interaction for the zoomed Image View that hides the view when tapped to reveal the Cover Flow for further selection.
Bunch of different ways to do this. Check out the Photo Gallery page in the Space Tours To Mars sample in the iAd Examples folder available for download where you downloaded iAd Producer.
Cheers,
-Mark