I can do one better. I can make it so that it only zooms when you mouse on the rectangle.

If you have 3.0 do this;

1. Start a new movie and create a clip. Add your Picture and square.

2. Add this code to the square in 2 actionscripts.

on(rollover){move="IN"}
on(rollout){Move="OUT")

3. Now on Frame 1 add this code.

if(this._xScale<900){
if(move=="IN"){this._xscale+=1;
this._yscale+=1;
}
}

if(this._xscale>0){
if(move=="OUT"){this._xscale-=1;
this._yscale-1;
}
}

4. Add a second Frame and add a Goto and Play Frame 1 action.

I dumped an example here http://jsnider.0catch.com/Scalein%20and%20out.html