I know I'm digging up an old thread, but it took me a little while to install this plugin on Windows. The problem for me was that it kept asking for the path to the GPG executable. There are so many EXE's that I didn't know which one it was looking for. When I finally clicked gpg2.exe then it worked.
Sounds stupid after the fact, but I just wanted to mention that it could be a bit clearer to the novice user installing it. Maybe you could set a filter in the browse window?