Hi! I'm another Betsy here
I've been thinking about exactly the same thing...a way of passing the time for the next year until we actually get to go on our cruise! Last week I was looking at the price of memory cards for our digital camera (a Canon A20...uses Compact Flash cards), and was astounded by how the prices have come down. In the
Best Buy and Circuit City ads, I saw 128 MB cards for around $40-45. We currently have a 64 MB one in our camera, and using medium resolution setting (looks great to us!), that can hold close to 100 pictures as I recall. Remember also that with a digital you can go through each night and dump all the duds, so you don't need to think of the numbers quite the same way as you would for regular film. So, I'd suggest taking a look at the cost of a second and larger capacity card--the ones that come with the cameras are usually pretty small...I think ours was 16 MB--as you may be pleased at the relatively low cost. Also, review the settings you are using and play with it a bit; medium resolution may be just fine, and you'll get a lot more on than with the highest resolution.
If you haven't done so already, you most definitely will want rechargeable batteries and a good recharger; especially if you use the display for taking the photo (as opposed to using the viewfinder) and have the display on most of the time, digital cameras suck up batteries at a rate you won't believe. We have a recharger we like that also has a car adapter, and carry one set of batteries in the camera, a second set in the case, and then still more for game boys, flashlights, etc. More dollars in the beginning, but way cheaper and more convenient in the end!