[PHP] [php] unable to use rar_open ()

[HELP!]

I have install the windows
php_rar.dll<http://kromann.info/php5_2-Release/php_rar.dll> extension
model in window  but I have problem using the functions

function extractZip( )
{
   $rar_file = rar_open('example.rar') or die("Failed to open Rar archive");
$entries_list = rar_list($rar_file);
 print_r($entries_list);
}
extractZip( );

*Fatal error*: Call to undefined function rar_open() in  on line *4*