Masking effect like this one? help

[color=#ffffff]smooth rollover scaling…or something???[/color]
just wondering what do they use to make the rollover upscaling downscaling or whatever u call it maybe mask…bla bla is so smooth …how??? AS or tweening? so cool
wanna be able to make a masking like this anyone help will be very appreciated

[color=#800080]http://www.group94.com/[/color]

thanks

PS… do they ever answer thier comments… u know?