referer = urldecode(($_SERVER['HTTP_REFERER'] ? $_SERVER['HTTP_REFERER'] : $_ENV['HTTP_REFERER']));
			$this->sep = (eregi('(\?q=|\?qt=|\?p=)', $this->referer)) ? '\?' : '\&';
		}
	}

	/**
	* Gets the search engine and keywords.
	*
	* @param  void
	* @return array
	*/
	function get_keys()
	{
		if (!empty($this->referer))
		{
			if (eregi('www\.google', $this->referer))
			{
				// Google
				preg_match('#' . $this->sep . 'q=(.*?)\&#si', $this->referer, $this->keys);
				$this->search_engine = 'Google';
			}
			else if (eregi('(yahoo\.com|search\.yahoo)', $this->referer))
			{
				// Yahoo
				preg_match('#' . $this->sep . 'p=(.*?)\&#si', $this->referer, $this->keys);
				$this->search_engine = 'Yahoo';
			}
			else if (eregi('search\.msn', $this->referer))
			{
				// MSN
				preg_match('#' . $this->sep . 'q=(.*?)\&#si', $this->referer, $this->keys);
				$this->search_engine = 'MSN';
			}
			else if (eregi('www\.alltheweb', $this->referer))
			{
				// AllTheWeb
				preg_match('#' . $this->sep . 'q=(.*?)\&#si', $this->referer, $this->keys);
				$this->search_engine = 'AllTheWeb';
			}
			else if (eregi('(looksmart\.com|search\.looksmart)', $this->referer))
			{
				// Looksmart
				preg_match('#' . $this->sep . 'qt=(.*?)\&#si', $this->referer, $this->keys);
				$this->search_engine = 'Looksmart';
			}
			else if (eregi('(askjeeves\.com|ask\.com)', $this->referer))
			{
				// AskJeeves
				preg_match('#' . $this->sep . 'q=(.*?)\&#si', $this->referer, $this->keys);
				$this->search_engine = 'AskJeeves';
			}
			else
			{
				$this->keys = 'Not available';
				$this->search_engine = 'Unknown';
			}
			return array(
				$this->referer,
				(!is_array($this->keys) ? $this->keys : $this->keys[1]),
				$this->search_engine
			);
		}
		else
		{
			return array();
		}
	}
}

?>

Example

get_keys();

if (count($keys))
{
	echo "Referring URL: $keys[0]
Keywords: $keys[1]
Search Engine: $keys[2]";
}

?>