Angela,
Welcome to Scubaboard! I took the same cruise in February of 07, and I was wishing that I had gone ahead and gotten SCUBA certified before I took the cruise. If it is the same one, it leaves out of San Juan, PR. My girlfriend and I snorkeled in Aruba & St. Thomas, and the whole time, I was wishing I had my SCUBA certification. Snorkeling is just a tease... Needless to say, I have my cert now, and I plan to go back to St. Thomas to do some diving. I saw lots of turtles and tons of fish, and we were just snorkeling.
Truly, the prices of equipment on the ship were not outrageous. I bought masks & fins & snorkels, and I later checked online for the same equipment, and all in all, I felt good about my purchase. Don't overload yourself with gear. I would recommend getting your own regulator and at least a rash suit. In Cozumel this past February, I bought a .5 mm wetsuit. That's right, 1/2 mm. I like it for the very reason mentioned above - jellyfish. My divemaster got a tenticle around his wrist and across his face, and he was not a happy camper. Upon investigation, I had a couple of tenticles around my wrist and one on my leg, but no stings... I am loving my .5 mm wetsuit at this point.
Royal Caribbean is a GREAT cruise line. I have been on a few cruises, and I really liked RC.
As a side note, if you are cruising out of Puerto Rico, take a couple of days and see the island. It would be a shame to not visit the 51st state... ;-)
