yeah, you need to add a mask to the track ABOVE the zooming clip.
i like to make my own in Photoshop,
but if it's just a one-off or a few then there is a free generator you can get, courtesy of ANDY MEES
here's his site:
[
web.mac.com]
look for "Andy?s Letterbox 2"
Andy's generator is TOTALY AWSOME!!!!
but the reason i prefer a photoshop DIY thingy is it seems to do better in the RealTime stakes,
and renders a bit faster (last time i used it, anyway)
cheers,
nick