Hi Jules,
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.
http://developer.apple.com/documentation/DeveloperTools/Conceptual/XcodeUserGuide/Contents/Resources/en.lproj/05_05_build_configs/chapter_32_section_6.html
Best regards,
Masanao Hayashi