My only xcode 4.3 sdk, how do ah?

I installed xcode 3.2.6, found that only 4.3 sdk, I want to use sdk 3.0 development, how to do ah? How to Add to xcode, ah?
Reply:
SDK 4.3 can also do a low version of the application, set the deployment target on the line
Reply:
Or download an older version of the sdk it. .
Give you a download link

http://alex-yang-xiansoftware-com.iteye.com/blog/1163146


Reply:
Set Deployment Target of 4.0 could occur 4.0 4.1 4.2 4.3 simulator directly in properties and targets of the project inside.
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4.3's certainly no problem, it is compatible with 3.0, not less than 3.0