if these libraries you downloaded are true PHP modules/extensions/libraries, you have to dynamically load them into your scripts.
Place the mcrypt/mhash stuff into your extensions folder under the php folder (c:\php\extensions).
NOTE: THE PHP PACKAGE FOR WINDOWS SHOULD HAVE ALREADY COME WITH THE MCRYPT LIBRARY! IF YOU DON'T SEE THE PHP_MCRYPT.DLL IN THE EXTENSIONS FOLDER, YOU NEED TO CONTACT THE PEOPLE WHO DISTRIBUTED THE VERSION OF PHP YOU HAVE AND CHEW THEM OUT.
Once you have the php_mcrypt.dll or whatever else the name of the library is, you have to load it into your script(s):
dl("extensions/php_mcrypt.dll"

;
or
dl("php_mcrypt.dll"

;
depending on your php.ini configuration.
If you got this far, you are ready to use mcrypt for encrypting/decrypting your strings/data.
If you need help using mcrypt, say so and I will be happy to assist. It is very simple.
Chad.