Fluid effect in letinmotion.com

hi…
i am a kinda noobie to flash i just wanted to know how they do that
fluid effect when you hover over the button or the water rippling effect superposed on the pix of the projectshowcase.

theres another cool site called advance flash.net who have lots of nice effects … what i can’t figure out is how do you go about superposing those effects without the background…

Thanks in advance!!!
:chinaman: