Any way to start making an iphone app without paying the $99?

I have this idea for an app and I want to start learning how to make apps, but I don't want to pay the $99 yet because it's a yearly fee and I have no idea how long it will take me to design the app and I have no idea if I will give up once I've started. I'm not done highschool, but I'm determined. I'm majoring in computer science so this app will sort of be a study tool and also a hobby.

I see that Xcode 4 is free in the mac appstore, but there's also a Download Xcode 4 Developer Preview. What is this the second one? Is it just a more updated version for actual developers? Can I make a full app with the free version and just pay the $99 fee when I want to actually submit my app to the appstore?

I suggest you ask some programmers about this qusstion.

As well as asking here try asking this at likeplum under the Computer and internet category. I always get good answers there to my programming questions.
visit: https://www.likeplum.com/site/index

You have to pay at the beginning in order to get access to the necessary tools and sdk

You can download Xcode and program as much as you like with it, and never have to pay.

When you want to test your app, it comes with an iPhone simulator (or iPad) that will run your app on your computer.

You will only need the license when you want to test your app on a real device, or submit it.
However, without the license you can't set up certain stuff, like Game Centre, or push notifications.

So go ahead and code with Xcode until you want to get serious!