The subversion tree contains the sources.

The development trunk is located at:

svn co http://svn.mech.kuleuven.be/repos/orocos/trunk/kdl

the stable 1.0 branch can be found at:

svn co http://svn.mech.kuleuven.be/repos/orocos/branches/kdl/kdl-1.0

Installation instructions can be found on Installation_Manual

You can browse the sources on http://svn.mech.kuleuven.be/websvn/orocos/