The Allegro Wiki is migrating to github at https://github.com/liballeg/allegro_wiki/wiki
sudo port install allegro
sudo port upgrade --enforce-variants libpng +universal
A universal binary install for libpng is required because Allegro is 32bit only, 64bit is not supported yet, maybe you need install other libraries as universal binaries too.
Compile from source:
- From tarballs: The source files you will need to compile Allegro on Mac OSX with XCode are the here in the second section (select the Linux versions):