Preloading question

I have a preloading question.
I want to make a website, that will have 3 buttons that preload a external swf in to the main movie.
I want the preloader to preload first and then show the new info, but while preloading the old info is still visible.

So lets so you have buttons contact Info portfolio
When i open my site it will automatically load contact. When i click info the content from contact is still visible only a preloader appears and starts preloading, when preloading is done the contact content disappears and the info content appears.

Something like this is done in
They keep the old background and first preload a new background before the old one disolves.

Can someone help me with this, maybe with a tutorial or a source file

thanks in advance