A good website is discover cruises.co.uk. This lists all the ships and destinations plus also gives details about the different ships; entertainment facilities, food and age ranges of passengers etc.
Http://www.cruisett.com/ports.php Try this website look for the port of call then select December 2008 from the list above and you will see which ships are where in that period. Now not all cruise lines allow this information on this website but hopefully the ship you are looking for will show up when you select one of the islands in the Caribbean, but you need to do this one island at a time, there might be a better site which will list the ship/ports/dates but not found one yet, best of luck.
Http://www.cruisett.com/today.php This site lets you look for the cruise line and the ship and might make it easier to follow which ever one you are looking for, have fun.
Thank you so much for your help. Much appreciated.