The minimum requirements to build Warzone are System 10.5 and Xcode 3.1.
If you do not have Xcode 3.1 you can get it for free at Apple's website.
http://developer.apple.com/technology/xcode.html
You will need a free ADC Membership to download Xcode.

This directory contains support files for the Mac OS X port of Warzone 2100.
Since April, 2007, The Mac OS X port has been built using an Xcode project
that automatically downloads and builds all necessary external libraries.
Also, since that time, the Mac OS X port has produced a universal binary
and has required Mac OS X 10.4 "Tiger" to run.

To build the game, just run the following command:
  xcodebuild -project Warzone.xcodeproj -target Warzone -configuration Release

There are two build configurations available.  'Release' is compiled
normally, while 'Debug' sets the DEBUG preprocessor flag and automatically
sets the game's debugging options to the equivalent of --debug all when
launched, unless overwritten with a --debug command-line option.  The
debugging output can be viewed with Console.app.