Well I'm going on the same cruise!! I've been to the Caribbean but of the islands listed have only been to Antigua, Tortola and St Kitts.
It is relativelty easy to make your own way around and according to the brochure, Fred Olsen also help you with port info and a shuttle bus where the town or beach is more than a 15 minute walk.
It is normally very easy to pick up a taxi at the ports, especially if you befriend another couple to share the coats. Taxis wait on the quayside. For Tortola, Cane Garden Bay is a must if you like beaches, with some magnificent views on the journey. Just ma ke quite sure you get back to the boat well before the departure time.
I'm sure you won't be disappointed with this itinery.
I have to agree with Taylor you will truely have a wonderful time I have travelled to the Caribbean many times and more often than not the local people are more than happy to help you. However ensure to keep an eye on the time and familiarise yourself with the times that the ship will be leaving port. www.Caribbean.com is a great site for looking up activities for your trip just choose from the islands list on the left the when it has loaded scroll towards the bottom of the page and it has a list stating things like duty free & Activities and Attractions, pick the one your interested in and it will show you people and place you can book with.
Hope this helps
St. John's Antigua....... get the tour that does Shirley Heights, Nelson's Dockyard & English Harbour. The wild side is great at Devil's Bridge. The island boasts 365 beaches, but a lovely pink sand one is on the way from the 'edge 0f the rainforest' tour - Darkwood. I seem to remember bieng told that all beaches are public, including the resort hotels.