If this were me, I'd buy an external drive, install a clean copy of MacOS 10.6 on that and then Xcode 3.2.6, which is the last version of Xcode that officially supports PPC development.
You then set your "MINIMUM_DEPLOYMENT_TARGET" for your project to 10.4. You'll also set the supported architectures to i386 & ppc.
The more interesting challenge will be to try to get the same project to build both iOS & Macintosh targets.