MovieClip movement on scroll page

Hi all,

I’d like to ask if anyone does know about any code for this situation:

I have a page with height of 2800px. On this page I place a menu up of the page. As I scroll the page down, the menu disappears ( it still stays up). What I need is the menu to remain on the level of the page, where I am just, while I am scrolling the page. Something like on the this website
By the way it doesn’t have to be menu, I mean any mc that I want it to be moving on that page like that.
Thanks for any idea.