As an architect for advanced functionality with Javascript?

I am creating an application using ASP.Net MVC and I need / need it to work with and without javascript included. The first sticking point for me is this: when the user clicks on the registration link, if they don't have javascript they should be sent to the registration page which has the main page stuff ... but if they have javascript allowed then I want the registration form (same from the registration page to go out to the div above the page and fade out the background ...

What is the best way to design this to keep it simple and minimize code duplication?