I read the O'Reilly book "Learning Cocoa" years ago and thought it useful. However, I've been programming C since the early 1980's. The book spends a lot of time on user interface (interface builder etc.) topics. Personally I don't like the MVC paradigm for user interfaces as it creates so much burocracy for what should be simple things. If you want to learn Objective-C itself, without dealing with user interfaces, there may be easier ways.
As for Xcode, note that a new release is expected soon which will integrate Interface Builder and should make the development process much smoother.