* Place the htmlpurifier folder in your drupal modules directory.

* Download HTML Purifier. If your host is running PHP 4, you will need to
  install the 2.1 series; please see this URL:
  
    http://htmlpurifier.org/download.html#PHP4
  
  If you're on PHP 5, use this URL:
  
    http://htmlpurifier.org/download.html

* IF YOU DOWNLOADED THE REGULAR OR LITE DISTRIBUTION:
  Extract the "library" folder and place it inside your modules/htmlpurifier
  directory.

* IF YOU DOWNLOADED THE STANDALONE DISTRIBUTION:
  Create a library folder in your modules/htmlpurifier directory.
  Then, extract the "htmlpurifier-x.y.z" folder and place its contents
  (HTMLPurifier.standalone.php and the standalone folder) inside the library
  folder. Rename HTMLPurifier.standalone.php to HTMLPurifier.auto.php.

* Go to Administer > Site building > Modules and enable this module

* You can now create a new input format or add the HTML Purifier to an 
  existing input format. It is recommended that you place HTML Purifier as 
  the last filter in the input format. Reorder the filters if necessary.