I'm not sure whether this is any help to you but....I'm travelling on Cunard's Queen Victoria (Transatlantic Crossing alongside QE2) to New York on 6th January 2008 which will be a 7 night voyage. NYC is obviously a long way from Fort Lauderdale however, on arrival in New York I am going straight to the airport and flying down to Orlando with American Airlines - at a cost of only £45 ! I have checked on the American Airlines website (aa.com) and there is a flight direct from New York to Fort Lauderdale on 13th January 2008 (the date Victoria arrives in NYC) at a cost of £54. Other than this, I don't know of any ships that will be crossing the Atlantic in January (of course, you can always select the QE2 if you prefer).
All the best. Tim.