Jaye614,
I have always paid for my room before I leave for the trip. Just call the Hotels Reservations dept., not Starwwod and tell them u would like to make a Payment to your reservation. I tell them to charge the amount I want to pay to the Credit card I used to reserve the room (which is my VISA debit card). It's always nice to arrive with my room paid for and then I don't feel so guilty about making charges at the resort to my room.
I am sure if got a better deal the amount of overpayment would be a credit to your bill-if it was still there after your stay it would be credited to your CC.
Maureen