i'm not sure what your background is or what you plan to do, but you might want a cocoa programming book as well if you want to write mac applications (and don't know how to already). those books seem to be just about the nuts and bolts of using the application xcode for those who want to delve deeper into it's features. i might be wrong.
i haven't seen any of those books so i can't offer any advice, but hillegasses' book is a good intro to objective-c.
it probably is fine just to stick with the cd unless there is something really important you need 2.4.1 for, and if you're just beginning, probably not.
hope this helps some.