I'm not a huge fan of using Captivate's built in animation because I find it a bit limiting. Another solution is to use javascript / css. If you run this code you should be able to scale your rectangle. Make sure you give the rectangle the id 'myRectangle' and keep the 'c' in the code. You can change the duration of the animation by modifying the duration number (which is in milliseconds)
A 4 pixel wide rectangle would need to be multiplied by 250 to get it to 1000, so I think this should work.
myRectanglec.animate([
{
transform: 'scaleY(1) scale (1)'
},
{
transform: 'scaleY(250) scale (250)'
}
], {duration: 1000, fill: 'forwards'});
In the future you can change things like easing, opacity, colour, rotation, and position.