Installing
To install this plugin, copy the .dll to the plugins directory created by the
Pidgin installer (usually C:\Program Files\Pidgin\plugins) or to your own
plugins directory (usually needs to be created as a subdirectory of
%APPDATA%\.purple).  
Using your own plugins directory is preferred, Pidgin's installer will delete the plugins directory when you upgrade Pidgin; thus the .purple directory is a safer location to preserve your plugins across Pidgin updates.


Running
After installing the plugin and enabling it, save all your passwords that you want to encrypt by going to each account and checking "Remember Password."  Open Tools->Windows Secure Passwords->Save & Encrypt Passwords.  This takes your cleartext passwords and encrypts them to a new file.
To test and make sure it is working correctly, restart Pidgin, and your accounts should load using the new decrypted passwords.


Compiling
Example documentation:
http://plugins.guifications.org/trac/wiki/PluginPack#HowdoIbuildonWindowsHowdoIbuildpluginsthatarentenabledbydefaultonWindows

Follow the Windows Pidgin Build Instructions on http://developer.pidgin.im/wiki/BuildingWinPidgin
Download the source and extract it to pidgin-VERSION/pidgin/plugins. In Cygwin, change into the plugins directory and run 
"make -f Makefile.mingw winsecure_password.dll" to compile the plugin. From there you can copy the .dll file for our plugin into the Pidgin plugins directory.  
You can also run "make -f Makefile.mingw install" to copy the plugin to the win32-install-dir created during the Pidgin make process.