Windows users download php_rar.dll at http://pecl.php.net/package/rar
0. click the DLL link for Windows
1. download php_rar.dll for your php version
2. copy php_rar.dll to the "ext" folder
3. append the following directive to the [php] section of your working php.ini, you can search "extension=" and append it to the last extension directive.
4. restart your web server and enjoy.