Xcode iPhone OS multiple versions

Question

Is there a way to add earlier versions of iphone os in xcode 3.1.2, so I can build by app for different os versions?

Answer 1

I'm not sure if it is because I have had older versions of Xcode, but I can Get Info on a project and change the "Base SDK" property to an older version and then build for that, e.g. 2.2.1