How to Encrypt and digitally sign your emails to secure them from prying eyes

If everyone in the world properly secured their email account there would be no spam. But yeah… never going to happen. That's more of a reason to encrypt and digitally sign our emails, but isn't using p2p security really expensive and really hard? Nope. It's actually free and easy with GnuPG. It's demonstrated on Mac OS X, but it's just as easy with Windows.