Get the latest release here, unpack the source and compile & install it:
tar -xvjpf portagemaster-xxx.tar.bz2
Also checkout the Requirements section below.
Installation is very much the same as with official source release. Instructions for accessing CVS repository can be found here.
cvs -z3 -d:pserver:firstname.lastname@example.org:/cvsroot/portagemaster co portagemaster
All the work was done on 1.4 Sun JDK, I have not tried others but you are quite welcome to experiment in that direction, and email me about the results. So its Sun JDK 1.4 for now.
From 0.1.6 release Apache-Ant and Jikes are required for compilation.
Obviously you will need Gentoo Linux with Portage properly installed.