NOTE: These work for 10.4.x and up. Not sure if they work for anything below.
Python 3.1 is required for Blender 2.5. Please download the appropriate package at http://www.python.org/download/releases/
Xcode, and Cmake 2.6-4
Apple's latest Xcode is bundled with a host of other tools, including gcc - which is vital for compiling. You can download the latest at http://developer.apple.com/mac/
The Cmake makefile generators can be found at http://www.cmake.org/cmake/resources/software.html.
NOTE : Currently, I can only compile successfully using Cmake version 2.6-4. 2.8-1 doesn't seem to link libraries properly.
Just download and install the unix version from http://sourceforge.net/projects/scons/files/