I tried to build SFML for x86_64 but it failed. That is due to the fact I'm using Mac OS X 10.4 SDK to keep compatibility for this OS version, which does not include every 64 bits versions of the libraries. But I wonder whether building for ppc, i386, x86_64 using the Mac OS X 10.5 SDK (and assuming I'm using features still present on Mac OS X 10.4) would work.