Something

$this->domain = explode(".", $_SERVER['HTTP_HOST']);

.....

function determineName() {

   if( sizeof($this->domain) == 3 ) {
	
      if( $this->domain[0] == "www" ) {
	return NULL;
      } else {
      return strtolower($this->domain[0]);
      } 
   } elseif( sizeof($this->domain) == 4 ) {
      return strtolower($this->domain[1]);
   }
}