If you don't want to buy the 99$ program, but still want to make your own apps and put them on your own iPhone/iPod Touch, you can jailbreak your iPhone to do it. This link shows you how to do that once you've jailbroken your iPhone, which you can figure out how to do here. You could just makes apps for yourself that way, or distribute them for free or for money on Cydia. You don't need a really good mac for development, just get a MacBook or a Mac Mini.
Note: Jailbreaking is not illegal, you can do what you want with your iPhone, its yours (as long as you don't pirate illegal cracked apps).
