One of the biggest investments you will make when you decide to start programming for iOS devices (iPad, iPod and iPhone) is to buy a Mac Machine. You could buy a Macbook Pro laptop, the iMac or Mac Pro desktops to do the job. However, there is another intriguing option. The Mac Mini. Apple call it a desktop computer but it is smaller than most laptops we know and love. It runs the regular Mac OS X Operating system (the current edition is called Mountain Lion). I have found that it is also among the cheapest Mac machines capable of developing and building iOS Apps. Of course you will also have to invest in peripherals like a monitor, keyboard and a mouse.
Once you have your hardware sorted out, you will need a development environment that will let you develop and test your applications. This will be the XCode Integrated Development environment. For Windows programmers unfamiliar with Mac programming, XCode is the Mac equivalent of the Visual Studio IDE. XCode is available for free and can be downloaded from the Mac App Store.
Your now all set to begin programming on the Mac for iOS devices. The official resource for Apple and Mac development is the Apple Developer Portal. This site is is very rich with content including videos, tutorials and sample applications. You will find iOS specific content here. You will have to register as an Apple developer to access some of this content. Registration is free. However, Apple does have several paid developer programs. Of interest to us are the iOS developer programs. The biggest advantage a paid iOS developer program gives you is that it will provide the tools you need to test your iOS apps on an actual device (like an iPad, iPod or iPhone) and then distribute it on the Apple App store when your ready. If you do not subscribe to the paid program, you will be able to test your app only on the iPad and iPhone emulators on the Mac machine. You will see that the iOS developer program options include an individual program for $99 a year as well as a Company program for $99 a year (they cost the same). The advantage with the the company program is that it allows you to register around 100 developers to develop apps at the same time and test them.
If you are just starting off, you could get away with the free registration for a while until you are comfortable with iOS programming.
You can start learning iOS programming concepts here. Specifically, this article walks you through all the learning you will have to go through in order produce iOS applications. The biggest skill you will need to acquire is that of programming with the Objective C language as this is the primary language you will be using for iOS programming. You will acquire other skills like memory management, UI design, using graphics libraries and tools as you go along. Hope you have a good time doing so.