When booking, and checking in, you can request a preference, but it will not always be honored. For example, CBR does rotating refurbishings of buildings, so a place you may want to stay may not be bookable. Otherwise, it seems like you are randomly assigned at check-in.
Now for my story: we did an 8-day land/sea package in Sept '00 (8 days because we tagged an extra on at the start of the trip) and chose CBR.
Beforehand, I looked up a CBR resort map, and chose a particular village (I can't recall which), but it was one that was convenient to Port Royale (the food/shopping court) and a small playground. It was important to me since we have small kids, still needed evening milk, wanted to minimize walking and wanted the playground.
On check-in, we were assigned to the same village where all cruise passengers were assigned. I asked to be changed, and they refused since all cruise passengers were in that village (which also happened to be a long walk from Port Royale).
Afterwards, I realized why they wanted all cruise passengers in the same place: luggage. When it's time to pick up luggage, they don't want to drive all over CBR picking up everything. They want it in one spot. Aruba, is it?
So, by all means, do your homework, and ask for your preferance. Maybe you'll get lucky.