My brother and sister-in-law got married on the Grand Princess in 12/2002. They had a wonderful experience. Very Professionally done! They had absolutely no complaints. I was there, and in my opinion, if I was to get married again, that's how I would do it. Once you have picked out the wedding package that you want, all you have to do is show up for the cruise and bring what you plan to wear for your wedding! Look into it, you won't be disappointed. One bit of advice, they only marry couples on sea days, so if you decide to go this route, book it early. Try to be the first couple to be married on the first sea day, my brother and his wife were, once all is said and done, with all nervousness set aside, you will still have the majority of your cruise to relax and enjoy yourselves!
Wishing you both all the best!
P.S. - One neat extra they did receive, was a very attractive map of the carribean with the location marked where they said "I Do".