Yes, GNUPG is the tool you should look for!! Its free and reliable, compatible with Windows. But a setup.exe under Windows isn't availalbe for download from
www.gnupg.org.
Here's what gnupg.org says
Windows 95/98/NT/2000/ME/XP with x86 CPU works fine (you need a special setup to build it).
- However, the same is available from sourceforge.net under a dead project.
- Also have a look at Windows Privacy Tray and Windows Privacy Tools.
- These all are based on the free gnupg. This article could also be a useful.
However, since now you have some hints, the most useful and informative link could be this.