Why don’t you add a juce.xcconfig to the Xcode project including following settings?
GCC_VERSION_ppc = 3.3
MACOSX_DEPLOYMENT_TARGET_ppc = 10.3
SDK_ROOT_ppc = /Developer/SDKs/MacOSX10.3.9.sdk
Probablly all developpers want to support Mac OS X 10.3.9 as well as 10.4.x, so this is very useful for JUCE developpers, I think.
About build configuration file, see below.