Pig 0.7 is out: http://pig.apache.org/releases.html
Java 1.6 or higher, preferably from Sun (http://java.sun.com/javase/downloads/index.jsp). Set JAVA_HOME to the root of your Java installation.
Ant build tool: http://ant.apache.org/
JUnit to run unit tests: http://junit.sourceforge.net/
Check out pig code from SVN: svn co http://svn.apache.org/repos/asf/pig/trunk/
Build the code from the top directory: ant. If the build is successful, you should see the pig.jar file created in that directory.
To validate your pig.jar run unit test: ant test
Pig requires Hadoop 0.20