I want to start developing Games for apple iPhone and iPads but I have some related questions. I have mac running MAC OS X Leopard 10.5.5. So only supported version of Xcode for Leopard 10.5.5 is Xcode 3 so I want to know:

Is it ok to start to develop in Xcode 3? Will it work on all iPhones and iPad versions?
Or should I have to buy new mac running Lion to install Xcode 4 and develop App on that?

What are the drawbacks of using Xcode 3?