My husband and I got married on the Carnival Victory last March. As an "encore" bride, I have to say that getting married on a cruise is definitely the way to go. Contact the different cruise lines you're interested in, or go on their websites. They have the information posted on there and will be more than happy to send it to you.
Once we settled on a line and a cruise, I called the wedding planners at the carnival and they literally handled everything for us from then on out. We were mailed a packet and literally checkmarked everything we wanted and they took care of the rest. On our wedding day, all we had to do was dress and meet the photographer - we couldn't be happier with the results.
We didn't have any guests, just the two of us, but I'm sure it would be just as easy.
BTW, go to the photo gallery and look for the pictues from our wedding that are posted there. The Carnival photographer did a great job.