Gpg4win is a port GNU PG. GNU PG provides a way to encrypt and sign data and communication using the OpenPGP standard. This port attempts to make GNU PG easy to install and use with Microsoft Windows.

Gpg4win: EMail Security Using GnuPG for Windows

One useful enhancement is a plugin for Microsoft Outlook 2003 (GPGol).

There is a Gpg4win regular version that includes the manuals while the light version does not.