you may want to start of with the very, very simple apps that are provided on developer.apple.com and see if this is actually for you, since books can be quite expensive.
if you find this interesting, or just want to start programming then i would go out (or in on the net) and look for an iphone programming for dummies type book which will illustrate the basics of whats needed, and then the book it self may recommend other books to advance to. i wouldnt suggest going straight to C/java/objective c/c++ whatever objected orientated language straight away as you may find it tedious, and not really know what you are doing.
by following what is essentially a tutorial you will be able to work with proper material based around iphone/ipod touch.
i would also recommend going over to tizag.com and learn some javascript as this will introduce you into the basics of every programming language, ie if statements, for, while, switch, etc and once you have been able to get a hang of javascript, go onto the SDK.
as i said, i highly recommend doing javascript and/or developer tutorials to make sure this is the right thing for you
hope that help
carlos