title: Where is the difference when creating the same app for iPhone and then iPhone4?
body: <p>Is anybody able to explain how do you create the same app for the two versions of the iPhone? I have been reading the Developer Guide and a couple of books but I can't figure where should I start at. The only difference i found is in the screenshots' sizes but really, what should I do different when buidling my app: 
  - is there a different process or feature in the SDK or Interface Builder? should i start building it for iPhone3, or iPhone4? Is it the same thing? How would I be able to make it available for both versions at once?
  Any feedback would be great.
  Thanks!</p>