@dynamicduo It doesn’t cost $100 to get the SDK, you can download it for free. The $100 allows you to transfer your apps to your phone for testing and things and then eventually allows you to submit it to the app store. If you just get the free SDK you can write your program and try it in the included iphone emulator, but thats as far as you can go really.
But as phoenyx and dynamicduo have said the programming knowledge is essential, if you don’t have this you should start with the basics in an Object Oriented language such as Java. iPhone apps are written in Objective-C, which you could start with, however I am not sure how good this is for a first language, probably just as good as any other, but someone else with that experience will have to tell you.