windows build:
open projects\2k5\libpng.sln in VS 2k5 and build the "Lib Release" target.

osx build: (also build.sh)
CC="clang -arch i386 -arch x86_64 -g -isysroot /Developer/SDKs/MacOSX10.6.sdk -mmacosx-version-min=10.5" \
AR_RC="libtool -static -o" \
make -f scripts/makefile.gcc

linux build
CC="/valve/bin/gcc-4.5 -fPIC -fvisibility=hidden -I../zlib-1.2.5 -L ../../lib/linux32/release" make -f scripts/makefile.gcc