I know this would be crazy to have feature!!! Is there a way where when the user enters the zip code do an automatch and fill the state and city ?

I was looking at http://daspecster.github.com/ziptastic/demo.html 

This is exactly what I want but in a VF page!!!

Can somebody guide me how to use the javscript inside the VF page/provide any other alternatives to this approach ?

Thanks a lot!!