Periodically the developers will decide that a good stable point in development has been reached and release a official version of the Network Security Toolkit. You should be able to find the files which have been released at:

http://sourceforge.net/project/showfiles.php?group_id=85467

To download the source files for a paritcular release, you simply download the source tarball having a file name similiar to nst-1.8.1.tar.gz (the 1.8.1 indicates the release). Once downloaded, you can extract the tarball in the directory of your choosing.

The following commands can be used to anonymously check out the lastest version (assuming you want them in your $HOME/nst directory):

[root@salsa root]# mkdir $HOME/nst
[root@salsa root]# cd $HOME/nst
[root@salsa nst]# cvs -d:pserver:anonymous@nst.cvs.sourceforge.net:/cvsroot/nst login
Logging in to :pserver:anonymous@nst.cvs.sourceforge.net:2401/cvsroot/nst
CVS password:
[root@salsa nst]# cvs -z3 -d:pserver:anonymous@nst.cvs.sourceforge.net:/cvsroot/nst co .

The anonymous checkout above will not permit you to commit any changes you may have happen to made. If you are a developer associated with the project, you should refer to the CVS Notes and Setting Up ssh notes available at the project web site. Once you've followed those instructions, you can use the following command to checkout the current source code:

[root@salsa root]# mkdir $HOME/nst
[root@salsa root]# cd $HOME/nst
[root@salsa nst]# nstcvs checkout .

During active development, other developers may commit changes to the source tree. At which point, the source code you are working with will become out of date. You can bring your area back up to date at any time using the commands shown below (assuming you specified the --sf-user USER option to the configure command):

[root@salsa root]# cd $HOME/nst
[root@salsa nst]# make update