Sorry to drag up an old thread, but I'm having the same problem on my Intel Mac with 10.5.8.  I get exactly the same error message, regarding the _fopen$UNIX2003 symbol not being found.  My machine has a 2Ghz Core Duo processor (note, not Core 2 Duo) with 2GB RAM.  I think it might be a 32-bit only processor.  Perhaps the problems with the latest pre-built BitCoin are related to that?