Rar is currently available through PECL » http://pecl.php.net/package/rar.
Also you can use the PECL installer to install the Rar extension, using the following command: pecl -v install rar.
You can always download the tar.gz package and install Rar by hand:
Example #1 Rar installation
gunzip rar-xxx.tgz tar -xvf rar-xxx.tar cd rar-xxx phpize ./configure && make && make install
Windows users will enable php_rar.dll inside of php.ini in order to use these functions. A DLL for this PECL extension is currently unavailable. See also the building on Windows section.