One time sliding nav

One time sliding nav

I have a requirement for a project that I am not sure I have ever seen before but basically I need to have a nav bar across the bottom of the screen on the home page, when the user clicks on a link the nav bar slides up the page locks into place and scrolls the content underneath to the appropriate page ( it's a vertical scrolling site ).  The rest of the session it doesn't move. Any idea how I can achieve this or has anyone seen this?

Thanks!
Sam