Main thing I recommend, make sure your Mac is recent or powerful  
enough to run Leopard well, and if you're planning to do any thing  
like RubyCocoa, you'll best off using Xcode 3 (though Xcode 2 is  
possible...) and the new Interface Builder is a very very different  
beast that seems a bit like a Macromedia app in terms of pallets and  
things...