Mosaic effect


i’m a newbie to Flash/AS.
I would like to create my website menu in flash and i was thinking to display some pictures, using a mosaic effect to transit from 1 picture to another one.

so as my pictures are 1000x300 px, i was thinking to have some random squares (50 x 50 px) which should play with their alpha value.
moreover, square should have a grey color, to allow a random grey alpha playing during display of pictures.

so this is my imagination… but where to start ?

could you help me please ?