You can also obtain the PPR source code by checking it out of CVS.
Assuming that you have CVS installed, here is the command to download the development branch for the stable (1.5x) version:
cvs -z3 -d:pserver:email@example.com:/cvsroot/ppr checkout ppr
The stable branch is receiving only bug fixes. It will differ little if at all from the last stable release.
And here is the command for the unstable (2.xx) version:
cvs -z3 -d:pserver:firstname.lastname@example.org:/cvsroot/ppr checkout -r BRANCH_2_0 ppr
Please keep in mind that major changes are going on in the development branch so it will have new bugs, undocumented incompatibilities, and may not even be buildable.