First, you'll need to get at least a basic familiarity with the C programming language on which iOS programming is based. I don't know of any online courses in C, but I'm sure you'll find several options if you do a web search. It's not impossible to dive right into iOS development without having any C experience, but I would't recommend it if you've never done any programming at all.
Once you have at least a grounding in C, you can find a number of good resources for learning to develop for iOS by doing a web search for "learning iOS development" and/or "learning iOS programming". Stanford University also offers a free course in iOS development through iTunes U, though the course many not be running at the time you're ready for it. You'll also want to know about Apple's resources:
Message was edited by: varjak paw - missed at first that you were interested in developing for iOS rather than Mac OS X.