Xcode 3 vs Xcode 4 when dealing with Objective-C

[sihne_mark]

I know how to use Xcode pretty well and I've mastered C++, and now I want to move onto Objective-C, however my Mac runs on Tiger(OS X 10.5) and I can only use Xcode 3. The problem with that is that I've ordered a book that assumes you have Xcode 4, and Apple updated Objective-C and so some things that are new do not work for Xcode 3(for example I cannot use command line tool and @autoreleasepool doesn't work either.