This is something you should check with your doctors surgery.
Thanks for your far from helpful answer that is a tad late.
I posted the question on 1st December 2007 and went on the cruise in April 2008.
Yes I knew that I could contact a doctor but I rather hoped to get the information from people that had completed such a cruise rather than waste a doctor's time.
You will not need a Yellow Fever jab for that area. Honduras and Belize are malaria areas and if you are going to go ashore after dark then there is a definite risk however if you wear long sleeves and trousers and use a good insect repellant you should be free from bites. No one can guarantee this. In general mosquitoes never seem to come on board ships so stay onboard for those two ports if you are really worried. The rest of the ports are currently free from malaria carrying mosquitoes. The advertising say "It only takes one bite" but the risk, if you are careful is small. Sorry ...Ida.