It depends on exactly what you want to achieve.
If you want something like their site, then a series of MovieClips in pre-arranged locations.
Create MOUSE_OVER events on each MovieClip.
In the event handler, create your Tweens (I would recommend buying and using TweenLite from Greensock).
Listen for MOUSE_OUT and tween COMPLETE events - so that when the event finishes you can display the text and also if the user rolls off the movie clip you can do a reverse tween to return the movie clip back to the beginning.
Break it down and start with just *1* movie clip.
Add the roll over event to, initially, just change it's colour (and size - width or height)
Then start adding more event listeners and handlers and increase the application complexity.