Distibution package

The latest distribution packages including official beta versions are found on Java DevNet.

From CVS (The Bleeding Edge)

Short answer:

cvs -d :pserver:guest@cvs.dev.java.net:/cvs login
(Use an empty password, just hit enter..)
cvs -d :pserver:guest@cvs.dev.java.net:/cvs checkout opensymphony
cvs -d :pserver:guest@cvs.dev.java.net:/cvs checkout webwork

optional:
cvs -d :pserver:guest@cvs.dev.java.net:/cvs checkout xwork

Note: One needs to have ivy in $ANT_HOME/lib, cause WebWork uses ivy to manage its library dependencies.

Long answer:
See Building Webwork for a detailed description, including information on Ivy and JDK compatibility.