Last night I've installed the Mac OS X Developer's Tool from Apple Developer Connection website. It did not come with my iBook. Or maybe it is but I just cannot find it. Anyway, it is a 300Mb download, and it includes the lot in the package - compiler for C/C++/Objective-C/Java, project builder, interface builder, lots of documentation and quite a few sameple applications. All installed under /Developer directory.
So far I have only tried to use the C compiler, which is gcc 3.1. I started the Project Builder and Interface Builder, but I have just browsed around. I can't imagine Apple is giving the whole developers' tools away for free - like if Microsoft is giving away the VisualStudio for free.
I am starting to read on Objective-C, and hopefully I will have time to get onto Mac OS X development.