Hi Clare & welcome.

There's a section from the main page "Private Guides". I found one thread related to sorrento

http://www.luxurycruisetalk.com/ubb/ultimatebb.php?ubb=get_topic;f=10;t=000019

We've used Renato Cuomo's limo service and had a very good experience twice in the Sorrento area. http://www.cuomonet.it

His website includes Capri but we've only used him from Sorrento. For Capri, we took the hydrofoil service (near where the tenders will take you from the ship) and got a taxi on the island.

I hope that helps. Enjoy your trip! It's a wonderful itinerary. Cheers, Anne