It would also really help to have some knowledge of Java because Obj-C is kinda a smash between C++and Java.
Apple has a lot of tutorials, app sources and Obj-C manuals at http://developer.apple.com
There are websites like http://cocoadevcentral.com/d/learn_objectivec/
(the main one http://cocoadevcentral.com/ )
I highly, highly .... highly recommend reading this book if your new to Obj-C http://www.amazon.com/Cocoa-Programming-Mac-OS-3rd/dp/0321503619
I am going to put all of my simple to intermediate Obj-C programs (and sources) on my website gscx.org too - once I get it up.