There is a CVS server on samba.org which contains the latest HOWTOs, userspace tools and testsuite. For casual browsing, you can use the Web Interface.
To grab the latest sources, you can do the following:
cvs -d :pserver:cvs@cvs.samba.org:/cvsroot login
cvs -d :pserver:cvs@cvs.samba.org:/cvsroot co netfilter
cvs update -d -P