XCode SDK Update

to deploy app on iOS5.1, XCode 3.4 or above is required. But Xcode 3.4 is only valid for MacOS Lion

tricks to run iOS5.1 SDK on Snow Leopard
http://www.iphonedevsdk.com/forum/iphone-sdk-development/100229-snow-leopard-sdk-5-1-a.html

XCode 3.4 is installed as a separate app on MacOS
to download the SDK5.1: Xcode > Preferences > Downloads > Components > iOS 5.0 Simulator