xcode - Compiling for older versions of Mac OS X -

I have recently started preparing applications for Mac, on my recent release, I'm working on OSX Great suggestions have been found for 10.5 because I am working for 10.6 and compiling it.

I tried to search for 10.5 SDK but could not find it anywhere to download it! How can I prepare my app for using older versions of Mac OS X using Xcode 2.2 and developing in 10.6?

Edit: ------ I say that I do not have the option to select different SDK because I have no other installed and my problem is not available Where to get those SDKs? Is not really aware of compiling for the old SDX

Again from the whole Xcode tool package download. After that, run the installer, and when you go to the screen that is called "standard install", instead of continuing, instead of continuing, press Customize in the right-hand corner. You must have the option of installing MacOSX10.5.sdk as well as MacOSX10.4u.sdk.