Creating semi-transparent clouds

[nzteacher]

Anyone know how to create realistic clouds in Flash? Not just using video or tweening static images, but something along the lines of the Stella McCartney section on the adidas.com site. On the homepage, go to Performance, then select the Stella McCartney link and enter her part of the site. The cloud effect is amazing - any idea on how to do it?

[gigabytes]

from my point of view, it looks like that it's just transparent static image.