Chances are, if you care about CVS, you're going to want to read the build instructions.
The CVS repository is browsable online.
For anonymous pserver access:
cvs -d :pserver:anonymous@cvs.codehaus.org:/scm/cvspublic co drools
Developers access CVS through ssh. Something along the lines of this should suffice:
export CVS_RSH=ssh
cvs -d developer_name@cvs.codehaus.org/scm/cvs co drools