Hey there,
I just quickly looked through the site, and I think all they did was make a layer visible and invisible when you click on the buttons. If this is what you’re talking about, I’m pretty sure that’s how it was done. I guess you could always import an .swf into another one and set it’s _alpha to 80% or something like that, but it’s more effort that you probably don’t need to put into it.
Have a good one,
Uth 