This script must be called using a form. Your form should point to this script. Your form tag must contain the following attributes :
<form action="http://fiveworlds.org/bbs/upload.cgi" method="post" enctype="multipart/form-data">
The method must equal post and the enctype must equal multipart/form-data. The action has to point to this script (on your server). If you are reading this, copy and paste the example above. It has the correct values.