Executing rtf as php-script with IIS

Hi, I want to execute a php-script, which file-extension ist .rtf. Though I entered .rtf in the mmc->iis-configuration as a fileextension for "php.exe %s %s" (and restarted the service) the server doesn't start php but sending the script uninterpreted back to client (in this case: ms-word). When I start php from the comandline like "php myfile.rtf" everything works fine and I get the wanted output (on the comandline). Simple question: where else to enter the fileextension? Thanks Kai