jQuery solution for a client's site
You could turn this into a general purpose plugin, but I'm not gonna go into that. There are also many good plugins that provide this functionality.

I'd ditch the IDs and just use the index of the current element as the reference.

You'll obviously still need a parent element with an ID, for nav and slides, so your code knows where they are.

Create class for active slide/nav, when a nav item is clicked, you get the index, multiply it by slide width/height, and animate. You get the corresponding slide with the index, so no need for IDs. Give the clicked element an active class. First step as soon as click happens would be to remove the active class so you can reassign it.

Then just put together some css using your parent elements class/ID.

Your code will be more generic, and your html will be cleaner.