When I look at the build settings for my new project in Xcode 4.2, I can change the "Deployment > iOS Deployment Target" to iOS 4.3, but under "Architecture > Base SDK", I am strictly limited to iOS 5.
Are there any other steps I need to take to ensure that my new app will run on iOS 4.3? How do I change the Base SDK?
When you install the iOS SDK, it removes any previously installed SDKs. That's why iOS 5 is your only SDK choice.
Setting the deployment target to iOS 4.3 is the way to ensure your app runs on 4.3. The deployment target is the earliest version of iOS that can run your app. You must make sure not to use any new iOS 5 technologies and methods or else the app won't run on 4.3.