apple style expanding search field in menu bar

I'm coding a website and I'm trying to replicate the effect on the apple.com where when you click to focus the search field in the menu bar, and the search field expands and the rest of the menu bar shrinks to accommodate it.

I've been trying various tricks with jquery kwicks, and also simply expanding a text field using the animate function in jquery but the effect is not the same. If someone could get me on the right track I'd very much appreciate it!

Best Daniel