I've attached a project http://www.mediafire.com/file/t7w1aalacb7kpay
which shows the slide in behaviour.
I've used the Window Styles from our real application.
To simulate other activity (to slow down the animation) I spawn 16 threads that sit and do something intensive but boring in the background.
The background for the app is a giant button - Click it and you should see the animation in (over 2-3 frames usually). You might not see it every time, so you may need to repeat to see the animation.
Any information would be very valuable.