The traditions way to check out the source is to check out the whole argouml project from http://argouml.tigris.org/svn/argouml/trunk. This includes the source code, tools, documentation and web-site, i.e. :

svn checkout http://argouml.tigris.org/svn/argouml/trunk argouml --username guest

If you only want to build argouml, and don't want anything else, you could just download the source code and the tools:

svn checkout http://argouml.tigris.org/svn/argouml/trunk/src http://argouml.tigris.org/svn/argouml/trunk/tools argouml --username guest

If you just want to build the documentation you can just check out the documentation xml files and the tools:

svn checkout http://argouml.tigris.org/svn/argouml/trunk/documentation http://argouml.tigris.org/svn/argouml/trunk/tools argouml --username guest

For the documentation you will also need the file default.properties from http://argouml.tigris.org/svn/argouml/trunk/src/argouml-app/default.properties.

If you only want to work with the web site, just check out the www directory:

svn checkout http://argouml.tigris.org/svn/argouml/trunk/www argouml/www --username guest

When using the "guest" account, use an empty password.