I found this company on the internet that does both transfers from the airport to the ship and private tours. The name of the guy is George Kokkotos. He has a site at http://www.greecetravel.com/taxi/, but for all I know, the whole thing may be a rip off.
Does anyone have any experience with using this particular guy, or have any recommendations for other tour guides? I need transfers from the airport and a day long tour of Athens as well. Any help is appreciated!