How to re create

hi all,

It’s been a while lol…
anyways i was woundering if somebody could explain how this site is created?

http://www.flashkit.com/movies/Interfaces/Sites/Cool_Fla-Amit_Das-12110/index.php

What I want to know is how he used a mask to give that nice effect to the BG…

Any help would be greaqt!!!