iPhoneUtilityClient apparently will work for you.
http://www.iphonealley.com/news/new-iphone-utility-brings-modding-to-ppc-users
Quote from this article:
"iPhoneUtilityClient allows users of both PowerPC and Intel Mac's play with their iPhone's OS, enabling such things as custom ringtones and UI modding."
	
		
			
		
		
	
				
			http://www.iphonealley.com/news/new-iphone-utility-brings-modding-to-ppc-users
Quote from this article:
"iPhoneUtilityClient allows users of both PowerPC and Intel Mac's play with their iPhone's OS, enabling such things as custom ringtones and UI modding."