I am an iPhone Developer. If you are referring to emulators that will allow you to use the Apple SDK, there are hacks that people use to get around buying a Mac. However, developers I know say it is a lot of trouble. I personally recommend if you want to develop for apple, then use Apple products.
Of course, if you want to do graphics, content or any kind of design work for mobile apps, no problem using your Windows PC. There are Apple guidelines that tell you how to create and prepare graphics. Do read the Apple documentation on their website also.