version: 2.0.1
source: http://www.libexpat.org/

Note: this is mainly to make sure we have one, and it's in a consistent location. In Mac OS X, libexpat is in X11. But on OS X Server, you don't normally install X11, yet libexpat is in the Apache 2 distribution on Server. Bleh. The X11 expat is a little out-of-date, and I don't know about Server's copy.

in expat source dir:

export MACOSX_DEPLOYMENT_TARGET=10.5
./configure --mandir=/usr/local/share/man \
CFLAGS="-Os -arch i386 -arch x86_64 -arch ppc -arch ppc64"

replace BYTEORDER line:

#ifdef __BIG_ENDIAN__
  #define BYTEORDER 4321
#else
  #define BYTEORDER 1234
#endif

replace WORDS_BIGENDIAN line:

#ifdef __BIG_ENDIAN__
  #define WORDS_BIGENDIAN 1
#else
  #undef WORDS_BIGENDIAN
#endif

Note: only BYTEORDER used in sources.

make
sudo make install

in expat source dir:

export MACOSX_DEPLOYMENT_TARGET=10.4
./configure --mandir=/usr/local/share/man \
CFLAGS="-Os -arch i386 -arch ppc"

If you are compiling on a PPC Mac, add "-isysroot /Developer/SDKs/MacOSX10.4u.sdk" to CFLAGS on the above configure line. ie:

CFLAGS="-Os -arch ppc -arch i386 -isysroot /Developer/SDKs/MacOSX10.4u.sdk"

same edits as Leopard

make
sudo make install

in expat source dir:

./configure --mandir=/usr/local/share/man
make
sudo make install