mozilla + enigmail + gpg. works on linux/....bsd and windows. in fact, on windows for whatever reason it is slightly easier to set up than on ..ix.
The article was excellent at describing how to do this stuff using ssl, but as it points out, for practical purposes, the certificate authority is unsatisfactory, and actually paying one of those commercial ventures is anathema to those of us who abhor the notion that the internet is simply a means of making us pay some corporation or another for everything we do. The FSF or some similar entity should provide some kind of root certificate. Then i'd buy it. And funding for them too.